/*  _              _     _                                             _       __      __      __   
   / \     _   _  | |_  | |__     ___    _ __   _    ___   _ __ ___   | | __  / /_    / /_    / /_  
  / _ \   | | | | | __| | '_ \   / _ \  | '__| (_)  / __| | '_ ` _ \  | |/ / | '_ \  | '_ \  | '_ \ 
 / ___ \  | |_| | | |_  | | | | | (_) | | |     _  | (__  | | | | | | |   <  | (_) | | (_) | | (_) |
/_/   \_\  \__,_|  \__| |_| |_|  \___/  |_|    (_)  \___| |_| |_| |_| |_|\_\  \___/   \___/   \___/ 
[Created Time:       2025-02-17 09:24:52]
[Last Modified Time: 2025-02-17 10:27:20] */
#ifdef LOCAL
#include<bits/stdc++.h>
#include"debug.h"
#else
#pragma GCC optimize("Ofast", "unroll-loops")
#include<bits/stdc++.h>
#define D(...) ((void)0)
#endif
using namespace std; using ll = long long;
#define For(i, j, k) for ( int i = (j) ; i <= (k) ; i++ )
#define Fol(i, j, k) for ( int i = (j) ; i >= (k) ; i-- )
namespace FastIO
{
#define USE_FastIO
// ------------------------------
// #define DISABLE_MMAP
// ------------------------------
#if ( defined(LOCAL) || defined(_WIN32) ) && !defined(DISABLE_MMAP)
#define DISABLE_MMAP
#endif
#ifdef LOCAL
	inline void _chk_i() {}
	inline char _gc_nochk() { return getchar(); }
	inline char _gc() { return getchar(); }
	inline void _chk_o() {}
	inline void _pc_nochk(char c) { putchar(c); }
	inline void _pc(char c) { putchar(c); }
	template < int n > inline void _pnc_nochk(const char *c) { for ( int i = 0 ; i < n ; i++ ) putchar(c[i]); }
#else
#ifdef DISABLE_MMAP
	inline constexpr int _READ_SIZE = 1 << 18; inline static char _read_buffer[_READ_SIZE + 40], *_read_ptr = nullptr, *_read_ptr_end = nullptr; static inline bool _eof = false;
	inline void _chk_i() { if ( __builtin_expect(!_eof, true) && __builtin_expect(_read_ptr_end - _read_ptr < 40, false) ) { int sz = _read_ptr_end - _read_ptr; if ( sz ) memcpy(_read_buffer, _read_ptr, sz); char *beg = _read_buffer + sz; _read_ptr = _read_buffer, _read_ptr_end = beg + fread(beg, 1, _READ_SIZE, stdin); if ( __builtin_expect(_read_ptr_end != beg + _READ_SIZE, false) ) _eof = true, *_read_ptr_end = EOF; } }
	inline char _gc_nochk() { return __builtin_expect(_eof && _read_ptr == _read_ptr_end, false) ? EOF : *_read_ptr++; }
	inline char _gc() { _chk_i(); return _gc_nochk(); }
#else
#include<sys/mman.h>
#include<sys/stat.h>
	inline static char *_read_ptr = (char *)mmap(nullptr, [] { struct stat s; return fstat(0, &s), s.st_size; } (), 1, 2, 0, 0);
	inline void _chk_i() {}
	inline char _gc_nochk() { return *_read_ptr++; }
	inline char _gc() { return *_read_ptr++; }
#endif
	inline constexpr int _WRITE_SIZE = 1 << 18; inline static char _write_buffer[_WRITE_SIZE + 40], *_write_ptr = _write_buffer;
	inline void _chk_o() { if ( __builtin_expect(_write_ptr - _write_buffer > _WRITE_SIZE, false) ) fwrite(_write_buffer, 1, _write_ptr - _write_buffer, stdout), _write_ptr = _write_buffer; }
	inline void _pc_nochk(char c) { *_write_ptr++ = c; }
	inline void _pc(char c) { *_write_ptr++ = c, _chk_o(); }
	template < int n > inline void _pnc_nochk(const char *c) { memcpy(_write_ptr, c, n), _write_ptr += n; }
	inline struct _auto_flush { inline ~_auto_flush() { fwrite(_write_buffer, 1, _write_ptr - _write_buffer, stdout); } } _auto_flush;
#endif
#define println println_ // don't use C++23 std::println
	template < class T > inline constexpr bool _is_signed = numeric_limits < T >::is_signed;
	template < class T > inline constexpr bool _is_unsigned = numeric_limits < T >::is_integer && !_is_signed < T >;
#if __SIZEOF_LONG__ == 64
	template <> inline constexpr bool _is_signed < __int128 > = true;
	template <> inline constexpr bool _is_unsigned < __uint128_t > = true;
#endif
	inline bool _isgraph(char c) { return c >= 33; }
	inline bool _isdigit(char c) { return 48 <= c && c <= 57; } // or faster, remove c <= 57
	constexpr struct _table {
#ifndef LOCAL
	int i[65536];
#endif
	char o[40000]; constexpr _table() :
#ifndef LOCAL
	i{},
#endif
	o{} {
#ifndef LOCAL
	for ( int x = 0 ; x < 65536 ; x++ ) i[x] = -1; for ( int x = 0 ; x <= 9 ; x++ ) for ( int y = 0 ; y <= 9 ; y++ ) i[x + y * 256 + 12336] = x * 10 + y;
#endif
	for ( int x = 0 ; x < 10000 ; x++ ) for ( int y = 3, z = x ; ~y ; y-- ) o[x * 4 + y] = z % 10 + 48, z /= 10; } } _table;
	template < class T, int digit > inline constexpr T _pw10 = 10 * _pw10 < T, digit - 1 >;
	template < class T > inline constexpr T _pw10 < T, 0 > = 1;
	inline void read(char &c) { do c = _gc(); while ( !_isgraph(c) ); }
	inline void read_cstr(char *s) { char c = _gc(); while ( !_isgraph(c) ) c = _gc(); while ( _isgraph(c) ) *s++ = c, c = _gc(); *s = 0; }
	inline void read(string &s) { char c = _gc(); s.clear(); while ( !_isgraph(c) ) c = _gc(); while ( _isgraph(c) ) s.push_back(c), c = _gc(); }
	template < class T, bool neg >
#ifndef LOCAL
	__attribute__((no_sanitize("undefined")))
#endif
	inline void _read_int_suf(T &x) { _chk_i(); char c; while
#ifndef LOCAL
	( ~_table.i[*reinterpret_cast < unsigned short *& >(_read_ptr)] ) if constexpr ( neg ) x = x * 100 - _table.i[*reinterpret_cast < unsigned short *& >(_read_ptr)++]; else x = x * 100 + _table.i[*reinterpret_cast < unsigned short *& >(_read_ptr)++]; if
#endif
	( _isdigit(c = _gc_nochk()) ) if constexpr ( neg ) x = x * 10 - ( c & 15 ); else x = x * 10 + ( c & 15 ); }
	template < class T, enable_if_t < _is_signed < T >, int > = 0 > inline void read(T &x) { char c; while ( !_isdigit(c = _gc()) ) if ( c == 45 ) { _read_int_suf < T, true >(x = -( _gc_nochk() & 15 )); return; } _read_int_suf < T, false >(x = c & 15); }
	template < class T, enable_if_t < _is_unsigned < T >, int > = 0 > inline void read(T &x) { char c; while ( !_isdigit(c = _gc()) ); _read_int_suf < T, false >(x = c & 15); }
	inline void write(bool x) { _pc(x | 48); }
	inline void write(char c) { _pc(c); }
	inline void write_cstr(const char *s) { while ( *s ) _pc(*s++); }
	inline void write(const string &s) { for ( char c : s ) _pc(c); }
	template < class T, bool neg, int digit > inline void _write_int_suf(T x) { if constexpr ( digit == 4 ) _pnc_nochk < 4 >(_table.o + ( neg ? -x : x ) * 4); else _write_int_suf < T, neg, digit / 2 >(x / _pw10 < T, digit / 2 >), _write_int_suf < T, neg, digit / 2 >(x % _pw10 < T, digit / 2 >); }
	template < class T, bool neg, int digit > inline void _write_int_pre(T x) { if constexpr ( digit <= 4 ) if ( digit >= 3 && ( neg ? x <= -100 : x >= 100 ) ) if ( digit >= 4 && ( neg ? x <= -1000 : x >= 1000 ) ) _pnc_nochk < 4 >(_table.o + ( neg ? -x : x ) * 4); else _pnc_nochk < 3 >(_table.o + ( neg ? -x : x ) * 4 + 1); else if ( digit >= 2 && ( neg ? x <= -10 : x >= 10 ) ) _pnc_nochk < 2 >(_table.o + ( neg ? -x : x ) * 4 + 2); else _pc_nochk(( neg ? -x : x ) | 48); else { constexpr int cur = 1 << __lg(digit - 1); if ( neg ? x <= -_pw10 < T, cur > : x >= _pw10 < T, cur > ) _write_int_pre < T, neg, digit - cur >(x / _pw10 < T, cur >), _write_int_suf < T, neg, cur >(x % _pw10 < T, cur >); else _write_int_pre < T, neg, cur >(x); } }
	template < class T, enable_if_t < _is_signed < T >, int > = 0 > inline void write(T x) { if ( x >= 0 ) _write_int_pre < T, false, numeric_limits < T >::digits10 + 1 >(x); else _pc_nochk(45), _write_int_pre < T, true, numeric_limits < T >::digits10 + 1 >(x); _chk_o(); }
	template < class T, enable_if_t < _is_unsigned < T >, int > = 0 > inline void write(T x) { _write_int_pre < T, false, numeric_limits < T >::digits10 + 1 >(x), _chk_o(); }
	template < size_t N, class ...T > inline void _read_tuple(tuple < T... > &x) { read(get < N >(x)); if constexpr ( N + 1 != sizeof...(T) ) _read_tuple < N + 1, T... >(x); }
	template < size_t N, class ...T > inline void _write_tuple(const tuple < T... > &x) { write(get < N >(x)); if constexpr ( N + 1 != sizeof...(T) ) _pc(32), _write_tuple < N + 1, T... >(x); }
	template < class ...T > inline void read(tuple < T... > &x) { _read_tuple < 0, T... >(x); }
	template < class ...T > inline void write(const tuple < T... > &x) { _write_tuple < 0, T... >(x); }
	template < class T1, class T2 > inline void read(pair < T1, T2 > &x) { read(x.first), read(x.second); }
	template < class T1, class T2 > inline void write(const pair < T1, T2 > &x) { write(x.first), _pc(32), write(x.second); }
	template < class T > inline auto read(T &x) -> decltype(x.read(), void()) { x.read(); }
	template < class T > inline auto write(const T &x) -> decltype(x.write(), void()) { x.write(); }
	template < class T1, class ...T2 > inline void read(T1 &x, T2 &...y) { read(x), read(y...); }
	template < class ...T > inline void read_cstr(char *x, T *...y) { read_cstr(x), read_cstr(y...); }
	template < class T1, class ...T2 > inline void write(const T1 &x, const T2 &...y) { write(x), write(y...); }
	template < class ...T > inline void write_cstr(const char *x, const T *...y) { write_cstr(x), write_cstr(y...); }
	template < class T > inline void print(const T &x) { write(x); }
	inline void print_cstr(const char *x) { write_cstr(x); }
	template < class T1, class ...T2 > inline void print(const T1 &x, const T2 &...y) { write(x), _pc(32), print(y...); }
	template < class ...T > inline void print_cstr(const char *x, const T *...y) { write_cstr(x), _pc(32), print_cstr(y...); }
	inline void println() { _pc(10); }
	inline void println_cstr() { _pc(10); }
	template < class ...T > inline void println(const T &...x) { print(x...), _pc(10); }
	template < class ...T > inline void println_cstr(const T *...x) { print_cstr(x...), _pc(10); }
}	using FastIO::read, FastIO::read_cstr, FastIO::write, FastIO::write_cstr, FastIO::println, FastIO::println_cstr;
using E = tuple < int, int, int, int >;
namespace small
{
	int o, jyc, eid[6][6], vis[1 << 15], fr[1 << 15]; E w[1 << 15]; bool used[6];
	vector < pair < int, E > > g[1 << 15]; queue < int > q;
	inline void dfs(int u, int e)
	{
		if ( used[u] ) return; used[u] = true;
		For(i, 0, 5) if ( i != u && e & ( 1 << eid[u][i] ) ) dfs(i, e);
	}
	inline void init()
	{
		For(i, 0, 5) For(j, i + 1, 5) eid[i][j] = eid[j][i] = o++;
		For(i, 0, ( 1 << 15 ) - 1) if ( __builtin_popcount(i) == 5 )
		{
			fill(used, used + 6, false), dfs(0, i);
			if ( count(used, used + 6, false) ) continue;
			For(a, 0, 5) For(b, 0, 5) if ( b != a && i & ( 1 << eid[a][b] ) )
				For(c, 0, 5) if ( c != a && c != b && i & ( 1 << eid[b][c] ) )
					For(d, a + 1, 5) if ( d != b && d != c && i & ( 1 << eid[c][d] ) ) o = i,
						o ^= ( 1 << eid[a][b] ) | ( 1 << eid[b][c] ) | ( 1 << eid[c][d] ),
						o |= ( 1 << eid[a][c] ) | ( 1 << eid[a][d] ) | ( 1 << eid[b][d] ),
						g[i].emplace_back(o, E(a, b, c, d));
		}
	}
	inline vector < E > bfs(int s, int t)
	{
		vis[s] = ++jyc, decltype(q)().swap(q), q.push(s);
		for ( int u ; q.size() ; )
		{
			u = q.front(), q.pop();
			for ( auto [v, damn] : g[u] ) if ( vis[v] != jyc )
			{
				fr[v] = u, w[v] = damn;
				if ( v == t )
				{
					vector < E > z; for ( ; v != s ; v = fr[v] ) z.emplace_back(w[v]);
					return reverse(z.begin(), z.end()), z;
				}
				vis[v] = jyc, q.push(v);
			}
		}
		return {};
	}
}
int n, u, v; bool g[109][109], used[109], ok; vector < E > ans;
int main()
{
	small::init(), read(n);
	For(i, 2, n) read(u, v), g[u][v] = g[v][u] = true;
	const auto op = [&](int a, int b, int c, int d) {
		ans.emplace_back(a, b, c, d);
		g[a][b] = g[b][a] = g[b][c] = g[c][b] = g[c][d] = g[d][c] = false;
		g[a][c] = g[c][a] = g[a][d] = g[d][a] = g[b][d] = g[d][b] =  true;
	};
	const auto zjy = [&] {
		For(i, 2, n) if ( g[1][i] ) For(j, 2, n) if ( g[i][j] )
			For(k, 2, n) if ( i != k && g[j][k] ) return op(1, i, j, k), true;
		return false;
	};
	while ( zjy() );
	u = 0;
	For(i, 2, n) if ( g[1][i] )
	{
		For(j, 2, n) if ( g[i][j] ) { u = i, v = j; break; }
		if ( u ) break;
	}
	if ( u )
	{
		if ( n == 5 )
		{
			ok = false;
			For(i, 2, n) if ( i != u && g[1][i] )
			{
				For(j, 2, n) if ( g[i][j] ) { op(v, u, 1, i), ok = true; break; }
				if ( ok ) break;
			}
		}
		else
		{
			const auto wsy = [&](int a, int b, int c, int d, int e) {
				vector < int > zsj = { a, b, c, d, e }; int o = 0, cyb = 0, zqs = 0;
				for ( int i : zsj )
				{
					For(j, 1, n)
						if ( j != a && j != b && j != c && j != d && j != e && g[i][j] ) { o = j; break; }
					if ( o ) break;
				}
				zsj.push_back(o);
				For(i, 0, 5) For(j, i + 1, 5) if ( g[zsj[i]][zsj[j]] ) cyb |= 1 << small::eid[i][j];
				zqs = cyb, zqs ^= 1 << small::eid[3][4], zqs |= 1 << small::eid[1][4];
				for ( auto [a, b, c, d] : small::bfs(cyb, zqs) ) op(zsj[a], zsj[b], zsj[c], zsj[d]);
			};
			const auto zjy = [&] {
				For(i, 2, n) if ( i != u && g[1][i] ) For(j, 2, n) if ( g[i][j] )
					return wsy(v, u, 1, i, j), true;
				return false;
			};
			while ( zjy() );
		}
	}
	println(ans.size()); for ( E i : ans ) println(i);
	return 0;
}
// 想上GM捏 想上GM捏 想上GM捏 想上GM捏 想上GM捏
// 伊娜可爱捏 伊娜贴贴捏