#include <bits/stdc++.h>

using namespace std;

/*
w[12345]  -->  [w1234]B  -->  12345B
[1234B]   -->  [12345]   -->  w1234
*/

signed main() {
    int n, m; scanf("%d%d", &n, &m);
    string S, T; cin >> S >> T;
    for (auto &c : S) c = (c == 'B' ? 'W' : 'B');
    for (auto &c : T) c = (c == 'B' ? 'W' : 'B');
    if (count(S.begin(), S.end(), 'W') > count(S.begin(), S.end(), 'B')) {
        for (auto &c : S) c ^= 'W' ^ 'B';
        for (auto &c : T) c ^= 'W' ^ 'B';
    }
    S = ' ' + S, T = ' ' + T;
    vector< pair<int, int> > res;
    deque<char> QS, QT;
    for (int i = 1; i <= m + 1; ++i) QS.push_back(S[i]);
    for (int i = n - m + 1; i <= n; ++i) QT.push_back(T[i]);
    int L1 = 1, R1 = m + 1, L2 = n - m + 1, R2 = n, flg = 0;
    while (1) {
        while  (QS.front() == 'B') {
            if (L1 == n) {flg = 1; break;}
            ++L1, ++R1, QS.pop_front(), QS.push_back(R1 > n ? 'B' : S[R1]);
        }
        if (flg) break;
        while  (QT.back() == 'W') {
            --L2, --R2, QT.pop_back(), QT.push_front(L2 < 1 ? 'W' : T[L2]);
        }
        res.push_back(make_pair(L1 % n + 1, (L2 + n - 1) % n + 1));
        res.push_back(make_pair(L1, (L2 + n - 1) % n + 1));
        QS.pop_front(), QS.push_back('B');
        QT.pop_back(), QT.push_front('W');
    }
    printf("%d\n", (int)res.size());
    for (auto [x, y] : res) printf("%d %d\n", x, y);
    return 0;
}