#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfenv>
#include <cfloat>
#include <chrono>
#include <cinttypes>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <initializer_list>
#include <iomanip>
#include <ios>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <streambuf>
#include <string>
#include <tuple>
#include <type_traits>
#include <variant>
#include <bit>
#include <compare>
#include <concepts>
#include <numbers>
#include <ranges>
#include <span>

#define int ll
#define INT128_MAX (__int128)(((unsigned __int128) 1 << ((sizeof(__int128) * __CHAR_BIT__) - 1)) - 1)
#define INT128_MIN (-INT128_MAX - 1)

#define clock chrono::steady_clock::now().time_since_epoch().count()

using namespace std;

template<class T1, class T2>
ostream& operator<<(ostream& os, const pair<T1, T2> pr) {
  return os << pr.first << ' ' << pr.second;
}
template<class T, size_t N>
ostream& operator<<(ostream& os, const array<T, N> &arr) {
  for(size_t i = 0; T x : arr) {
    os << x;
    if (++i != N) os << ' ';
  }
  return os;
}
template<class T>
ostream& operator<<(ostream& os, const vector<T> &vec) {
  for(size_t i = 0; T x : vec) {
    os << x;
    if (++i != size(vec)) os << ' ';
  }
  return os;
}
template<class T>
ostream& operator<<(ostream& os, const set<T> &s) {
  for(size_t i = 0; T x : s) {
    os << x;
    if (++i != size(s)) os << ' ';
  }
  return os;
}
template<class T1, class T2>
ostream& operator<<(ostream& os, const map<T1, T2> &m) {
  for(size_t i = 0; pair<T1, T2> x : m) {
    os << x;
    if (++i != size(m)) os << ' ';
  }
  return os;
}

#ifdef DEBUG
#define dbg(...) cerr << '(', _do(#__VA_ARGS__), cerr << ") = ", _do2(__VA_ARGS__)
template<typename T> void _do(T &&x) { cerr << x; }
template<typename T, typename ...S> void _do(T &&x, S&&...y) { cerr << x << ", "; _do(y...); }
template<typename T> void _do2(T &&x) { cerr << x << endl; }
template<typename T, typename ...S> void _do2(T &&x, S&&...y) { cerr << x << ", "; _do2(y...); }
#else
#define dbg(...)
#endif

using ll = long long;
using ull = unsigned long long;
using ldb = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
//#define double ldb

template<typename T> using min_heap = priority_queue<T, vector<T>, greater<T>>;
template<typename T> using max_heap = priority_queue<T>;

template<ranges::forward_range rng, class T = ranges::range_value_t<rng>, class OP = plus<T>>
void pSum(rng &&v) {
  if (!v.empty())
    for(T p = v[0]; T &x : v | views::drop(1))
      x = p = OP()(p, x);
}
template<ranges::forward_range rng, class T = ranges::range_value_t<rng>, class OP>
void pSum(rng &&v, OP op) {
  if (!v.empty())
    for(T p = v[0]; T &x : v | views::drop(1))
      x = p = op(p, x);
}

template<ranges::forward_range rng>
void Unique(rng &v) {
  ranges::sort(v);
  v.resize(unique(v.begin(), v.end()) - v.begin());
}

template<ranges::random_access_range rng>
rng invPerm(rng p) {
  rng ret = p;
  for(int i = 0; i < ssize(p); i++)
    ret[p[i]] = i;
  return ret;
}

template<ranges::random_access_range rng, ranges::random_access_range rng2>
rng Permute(rng v, rng2 p) {
  rng ret = v;
  for(int i = 0; i < ssize(p); i++)
    ret[p[i]] = v[i];
  return ret;
}

template<bool directed>
vector<vector<int>> readGraph(int n, int m, int base) {
  vector<vector<int>> g(n);
  for(int i = 0; i < m; i++) {
    int u, v; cin >> u >> v;
    u -= base, v -= base;
    g[u].emplace_back(v);
    if constexpr (!directed)
      g[v].emplace_back(u);
  }
  return g;
}

template<class T>
void setBit(T &msk, int bit, bool x) {
  msk = (msk & ~(T(1) << bit)) | (T(x) << bit);
}
template<class T> void flipBit(T &msk, int bit) { msk ^= T(1) << bit; }
template<class T> bool getBit(T msk, int bit) { return msk >> bit & T(1); }

template<class T>
T floorDiv(T a, T b) {
  if (b < 0) a *= -1, b *= -1;
  return a >= 0 ? a / b : (a - b + 1) / b;
}
template<class T>
T ceilDiv(T a, T b) {
  if (b < 0) a *= -1, b *= -1;
  return a >= 0 ? (a + b - 1) / b : a / b;
}

template<class T> bool chmin(T &a, T b) { return a > b ? a = b, 1 : 0; }
template<class T> bool chmax(T &a, T b) { return a < b ? a = b, 1 : 0; }

template<class V, V(*base)(int), class E, E(*addEdge)(const V&, int eid),
E(*op)(const E&, const E&), V(*addVertex)(const E&, int vid)>
vector<V> rerootingDP(vector<array<int, 2>> e) {
  int n = ssize(e) + 1;
  vector<vector<int>> g(n);
  for(int i = 0; auto [u, v] : e)
    g[u].emplace_back(i), g[v].emplace_back(i++);

  vector<V> data(n);
  for(int v = 0; v < n; v++) data[v] = base(v);
  auto precalc = [&](int v, int p, auto &&self) -> void {
    bool leaf = true;
    E prod;
    for(int eid : g[v]) {
      int x = e[eid][0] ^ e[eid][1] ^ v;
      if (x == p) continue;
      self(x, v, self);
      if (leaf)
        prod = addEdge(data[x], eid), leaf = false;
      else
        prod = op(prod, addEdge(data[x], eid));
    }
    if (!leaf) data[v] = addVertex(prod, v);
  };

  precalc(0, -1, precalc);

  vector<V> ret(n);
  auto reroot = [&](int v, int p, auto &&self) -> void {
    int deg = ssize(g[v]);
    vector<E> pre(deg), suf(deg);
    for(int i = 0; int eid : g[v]) {
      int x = e[eid][0] ^ e[eid][1] ^ v;
      pre[i] = suf[i] = addEdge(data[x], eid), i++;
    }
    for(int i = 1; i < deg; i++) pre[i] = op(pre[i - 1], pre[i]);
    for(int i = deg - 2; i >= 0; i--) suf[i] = op(suf[i], suf[i + 1]);
    V tmp = data[v];
    ret[v] = data[v] = (deg ? addVertex(suf[0], v) : base(v));
    for(int i = 0; int eid : g[v]) {
      int x = e[eid][0] ^ e[eid][1] ^ v;
      if (x != p) {
        bool leaf = true;
        E prod;
        if (i > 0) prod = pre[i - 1], leaf = false;
        if (i + 1 < deg) prod = (leaf ? suf[i + 1] : op(prod, suf[i + 1])), leaf = false;
        V tmp2 = data[v];
        data[v] = (leaf ? base(v) : addVertex(prod, v));
        self(x, v, self);
        data[v] = tmp2;
      }
      i++;
    }
    data[v] = tmp;
  };

  reroot(0, -1, reroot);

  return ret;
}

struct V {
  int h, pot, dp;
};

V base(int) {
  return {0, 0, 1};
}

struct E {
  int mx_h, sum_pot, sum_dp, mn_pot, cnt_child;
};

const int C = 1ll << 52;
E addEdge(const V& v, int) {
  return {v.h, min(2 * v.pot + 1, C), v.dp, min(2 * v.pot + 1, C), 1};
}

E op(const E& a, const E &b) {
  return {max(a.mx_h, b.mx_h), min(C, a.sum_pot + b.sum_pot), min(a.sum_dp + b.sum_dp, C), min(a.mn_pot, b.mn_pot), a.cnt_child + b.cnt_child};
}

V addVertex(const E& e, int) {
  return {e.mx_h + 1, e.sum_pot, min(e.sum_dp + e.sum_pot + (e.cnt_child >= 2 ? e.mn_pot : 0ll) + 1, C)};
}

void NIE() {
  cout << "NIE\n";
  exit(0);
}

signed main() {
  ios::sync_with_stdio(false), cin.tie(NULL);

  int n, m; cin >> n >> m;
  vector<array<int, 2>> e(m);
  for(auto &[u, v] : e) {
    cin >> u >> v;
    u--, v--;
  }

  if (m != n - 1) NIE();

  if (n == 1) {
    cout << 0 << '\n';
    return 0;
  }

  vector<int> deg(n);
  for(auto [u, v] : e) deg[u]++, deg[v]++;

  for(int i = 0; i < n; i++)
    if (deg[i] > 3)
      NIE();

  if (ranges::min(deg) == 3) NIE();

  auto dp = rerootingDP<V, base, E, addEdge, op, addVertex>(e);

  int ans = C;
  for(int v = 0; v < n; v++) {
    if (deg[v] > 2) continue;
    if (deg[v] == 1 and dp[v].h <= 32) chmin(ans, dp[v].dp - dp[v].pot - 1);
    if (deg[v] == 2 and dp[v].h < 32) chmin(ans, dp[v].dp);
  }

  cout << ans << '\n';

  return 0;
}