#include <bits/stdc++.h>

using namespace std;

const int N = 505;

int f[N][N], g[N][N], s[2][N], o[N];

signed main() {
    int n, C; scanf("%d%d", &n, &C);
    string S, T; cin >> S >> T;
    S = ' ' + S, T = ' ' + T;
    vector<int> sa, sb[2];
    for (int i = 1; i <= n; ++i) {
        if (S[i] == '2') sa.push_back(i);
        if (T[i] == '2') sb[i & 1].push_back(i), s[i & 1][i] = 1;
        s[0][i] += s[0][i - 1], s[1][i] += s[1][i - 1];
    }
    memset(f, 0x3f, sizeof(f));
    f[0][0] = 0;
    int c1 = sb[0].size(), c2 = sb[1].size();
    for (int i = 0; i <= c1; ++i) {
        for (int j = 0; j <= c2; ++j) {
            if (i != c1) {
                int d = abs(sb[0][i] - sa[i + j]), nf = f[i][j] + (d + 1) / 2 * C + d / 2 * 4 + d % 2 * 3 + max(s[1][sb[0][i]] - j, 0);
                if (nf < f[i + 1][j]) {
                    f[i + 1][j] = nf, g[i + 1][j] = 0;
                }
            }
            if (j != c2) {
                int d = abs(sb[1][j] - sa[i + j]), nf = f[i][j] + (d + 1) / 2 * C + d / 2 * 4 + d % 2 * 3 + max(s[0][sb[1][j]] - i, 0);
                if (nf < f[i][j + 1]) {
                    f[i][j + 1] = nf, g[i][j + 1] = 1;
                }
            }
        }
    }
    for (int i = c1, j = c2; i || j; ) {
        if (!g[i][j]) --i, o[sa[i + j]] = sb[0][i];
        else --j, o[sa[i + j]] = sb[1][j];
    }
    vector< pair<int, int> > res;
    for (int i = n; i >= 1; --i) {
        if (o[i] && o[i] > i) {
            for (int j = i; j != o[i]; ) {
                int tj = j + (j + 1 == o[i] ? 1 : 2);
                res.push_back({j, tj}), j = tj;
            }
        }
    }
    for (int i = 1; i <= n; ++i) {
        if (o[i] && o[i] < i) {
            for (int j = i; j != o[i]; ) {
                int tj = j - (j - 1 == o[i] ? 1 : 2);
                res.push_back({tj, j}), j = tj;
            }
        }
    }
    printf("%d\n", (int)res.size());
    for (auto x : res) printf("%d %d\n", x.first, x.second);
    return 0;
}