#pragma GCC optimize(3, "unroll-loops", "no-stack-protector")
#define atsum(l, r) accumulate(l, r, 0)
#include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/hash_policy.hpp>
using namespace std;
using ll = long long;
using ull = unsigned long long;
constexpr int inf = 0x3f3f3f3f;
constexpr ll INF = 0x3f3f3f3f3f3f3f3f;
template <typename T>
inline void chkmin(T &x, T y) {
    x = min(x, y);
}
template <typename T>
inline void chkmax(T &x, T y) {
    x = max(x, y);
}
namespace FastIO {
// ------------------------------
#define IN_HAS_NEG
#define OUT_HAS_NEG
#define CHK_EOF
#define DISABLE_MMAP
// ------------------------------
#if __cplusplus < 201400
#error Please use C++14 or higher.
#endif
#if __cplusplus > 201700
#define INLINE_V inline
#else
#define INLINE_V
#endif
#if (defined(LOCAL) || defined(_WIN32)) && !defined(DISABLE_MMAP)
#define DISABLE_MMAP
#endif
#ifndef DISABLE_MMAP
#include <sys/mman.h>
#endif
#ifdef LOCAL
inline char gc() { return getchar(); }
inline void pc(char c) { putchar(c); }
#else
#ifdef DISABLE_MMAP
INLINE_V constexpr int _READ_SIZE = 1 << 18;
INLINE_V static char _read_buffer[_READ_SIZE], *_read_ptr = nullptr,
                                               *_read_ptr_end = nullptr;
inline char gc() {
    if (__builtin_expect(_read_ptr == _read_ptr_end, false)) {
        _read_ptr = _read_buffer;
        _read_ptr_end =
            _read_buffer + fread(_read_buffer, 1, _READ_SIZE, stdin);
#ifdef CHK_EOF
        if (__builtin_expect(_read_ptr == _read_ptr_end, false)) return EOF;
#endif
    }
    return *_read_ptr++;
}
#else
INLINE_V static const char *_read_ptr =
    (const char *)mmap(nullptr, INT_MAX, 1, 2, 0, 0);
inline char gc() { return *_read_ptr++; }
#endif
INLINE_V constexpr int _WRITE_SIZE = 1 << 18;
INLINE_V static char _write_buffer[_WRITE_SIZE], *_write_ptr = _write_buffer;
inline void pc(char c) {
    *_write_ptr++ = c;
    if (__builtin_expect(_write_buffer + _WRITE_SIZE == _write_ptr, false)) {
        fwrite(_write_buffer, 1, _write_ptr - _write_buffer, stdout);
        _write_ptr = _write_buffer;
    }
}
INLINE_V struct _auto_flush {
    ~_auto_flush() {
        fwrite(_write_buffer, 1, _write_ptr - _write_buffer, stdout);
    }
} _auto_flush;
#endif
#ifdef CHK_EOF
inline bool _isdigit(char c) { return (c & 16) && c != EOF; }
inline bool _isgraph(char c) { return c > 32 && c != EOF; }
#else
inline bool _isdigit(char c) { return c & 16; }
inline bool _isgraph(char c) { return c > 32; }
#endif
template <class T>
INLINE_V constexpr bool _is_integer = numeric_limits<T>::is_integer;
template <class T>
INLINE_V constexpr bool _is_signed = numeric_limits<T>::is_signed;
template <class T>
INLINE_V constexpr bool _is_unsigned = _is_integer<T> && !_is_signed<T>;
template <>
INLINE_V constexpr bool _is_integer<__int128> = true;
template <>
INLINE_V constexpr bool _is_integer<__uint128_t> = true;
template <>
INLINE_V constexpr bool _is_signed<__int128> = true;
template <>
INLINE_V constexpr bool _is_unsigned<__uint128_t> = true;
#undef INLINE_V
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();
}
#ifdef IN_HAS_NEG
template <class T, enable_if_t<_is_signed<T>, int> = 0>
inline void read(T &x) {
    char c = gc();
    bool f = true;
    x = 0;
    while (!_isdigit(c)) {
        if (c == 45) f = false;
        c = gc();
    }
    if (f)
        while (_isdigit(c)) x = x * 10 + (c & 15), c = gc();
    else
        while (_isdigit(c)) x = x * 10 - (c & 15), c = gc();
}
template <class T, enable_if_t<_is_unsigned<T>, int> = 0>
#else
template <class T, enable_if_t<_is_integer<T>, int> = 0>
#endif
inline void read(T &x) {
    char c = gc();
    while (!_isdigit(c)) c = gc();
    x = 0;
    while (_isdigit(c)) x = x * 10 + (c & 15), c = gc();
}
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);
}
#ifdef OUT_HAS_NEG
template <class T, enable_if_t<_is_signed<T>, int> = 0>
inline void write(T x) {
    char buffer[numeric_limits<T>::digits10 + 1];
    int digits = 0;
    if (x >= 0) do
            buffer[digits++] = (x % 10) | 48, x /= 10;
        while (x);
    else {
        pc(45);
        do buffer[digits++] = -(x % 10) | 48, x /= 10;
        while (x);
    }
    while (digits) pc(buffer[--digits]);
}
template <class T, enable_if_t<_is_unsigned<T>, int> = 0>
#else
template <class T, enable_if_t<_is_integer<T>, int> = 0>
#endif
inline void write(T x) {
    char buffer[numeric_limits<T>::digits10 + 1];
    int digits = 0;
    do buffer[digits++] = (x % 10) | 48, x /= 10;
    while (x);
    while (digits) pc(buffer[--digits]);
}
template <int N>
struct _tuple_io_helper {
    template <class... T>
    static inline void _read(tuple<T...> &x) {
        _tuple_io_helper<N - 1>::_read(x), read(get<N - 1>(x));
    }
    template <class... T>
    static inline void _write(const tuple<T...> &x) {
        _tuple_io_helper<N - 1>::_write(x), pc(32), write(get<N - 1>(x));
    }
};
template <>
struct _tuple_io_helper<1> {
    template <class... T>
    static inline void _read(tuple<T...> &x) {
        read(get<0>(x));
    }
    template <class... T>
    static inline void _write(const tuple<T...> &x) {
        write(get<0>(x));
    }
};
template <class... T>
inline void read(tuple<T...> &x) {
    _tuple_io_helper<sizeof...(T)>::_read(x);
}
template <class... T>
inline void write(const tuple<T...> &x) {
    _tuple_io_helper<sizeof...(T)>::_write(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 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) {
    print(x), pc(32), print(y...);
}
template <class... T>
inline void print_cstr(const char *x, const T *...y) {
    print_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);
}
}  // namespace FastIO
using namespace FastIO;
template <typename T>
inline void clear(T &x) {
    T y;
    swap(x, y);
}
const int N = 1e6 + 10;
int l[N], r[N], n;
char str[N];
pair<int, int> block[N];
int lb[N], rb[N], bc;
inline void delp(int x) { l[r[x]] = l[x], r[l[x]] = r[x]; }
inline void delpb(int x) { 
    lb[rb[x]] = lb[x], rb[lb[x]] = rb[x];
}
vector<pair<int, int> > res;
inline int realdel(int x) {
    // cerr << "find del:" << ' ' << x << ' ' << lb[x] << ' ' << block[lb[x]].second << ' ' << block[x].second << ' '<< block[x].first << endl;
    int c = block[lb[x]].second + 1, cnt = 0;
    int kl = lb[x];
    for (int i = block[x].first; ; i = r[i]) {
        delp(i), ++cnt;
        // cerr << "find cdel:" << i << endl;
        if (i == block[x].second) break;
    }
    // cerr << "find cnt qwq:" << cnt << endl;
    if (cnt % 3 == 2) res.emplace_back(c, 2), cnt -= 2;
    if (cnt % 3 == 0) {
        while (cnt) res.emplace_back(c, 3), cnt -= 3;
    } else if (cnt % 3 == 1) {
        cnt -= 4, res.emplace_back(c, 2), res.emplace_back(c, 2);
        while (cnt) res.emplace_back(c, 3), cnt -= 3;
    }
    r[block[lb[x]].second] = block[rb[x]].first;
    l[block[rb[x]].first] = block[lb[x]].second;
    block[lb[x]].second = block[rb[x]].second;
    delpb(x), delpb(rb[x]);
    return kl;
}
inline bool judge(int x) { return block[x].first == block[x].second; }
int pb[N], cb[N], sp[N];
inline void work(int L, int R) {
    // cerr << "find work:" << L << ' ' << R << endl;
    int mid = L + R >> 1;
    int pl = mid, pr = mid;
    assert(R ^ L ^ 1 & 1);
    while (judge(pl)) pl--;
    while (judge(pr)) pr++;
    int c = mid - pl;
    // cerr << "find c:" << c << endl;
    int cc = R - L + 1;
    while (c--) pr = realdel(pr), cc -= 2;
    while (cc > -1) pl = realdel(pl), cc -= 2;
    assert(cc == -1);
}
int main() {
    read(n), read_cstr(str + 1);
    l[n + 1] = n, r[0] = 1;
    for (int i = 1; i <= n; i++) l[i] = i - 1, r[i] = i + 1;
    for (int l = 1; l <= n;) {
        int r = l;
        while (r < n && str[r + 1] == str[l]) ++r;
        block[++bc] = {l, r}, lb[bc] = bc - 1, rb[bc] = bc + 1;
        l = r + 1;
    }
    lb[bc + 1] = bc, rb[0] = 1;
    for (int i = bc; i; i--)
        pb[i] = block[i].first == block[i].second ? pb[i + 1] + 1 : 0;
    for (int i = 1; i <= bc; i++)
        sp[i] = block[i].first == block[i].second ? sp[i - 1] + 1 : 0;
    block[bc + 1] = {n + 1, n + 1};
    // cerr << "after there" << endl;
    if (bc & 1 ^ 1) {
        for (int i = 1; i <= bc; i += 2)
            if (!(sp[i] >= (i >> 1) && judge(i + 1 >> 1)) &&
                !(pb[i + 1] >= (bc - i >> 1) && judge(bc + i + 1 >> 1))) {
                // cerr << "find i:" << i << endl;
                work(i + 1, bc);
                // cerr << "find r1:" << r[1] << ' ' << block[1].second << endl;
                if (block[i].second == n + 1) block[i].second = l[block[i].second], rb[i] = bc + 1, lb[bc + 1] = i;
                work(1, i);
                println(res.size());
                for (auto [l, r] : res) println(l, r);
                return 0;
            }
        return println("-1"s), 0;

    } else {
        if (pb[1] >= (bc >> 1) &&
            block[(bc >> 1) + 1].first == block[(bc >> 1) + 1].second)
            return println("-1"s), 0;
        work(1, bc);
        println(res.size());
        for (auto [l, r] : res) println(l, r);
    }
    return 0;
}
/*
9
ABAABBBAA
*/
/*
2 2 1

15
AABABAABABAABAB

2 11121112111
*/