#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)




int N, M; string S, T;
//-----------------------------------------------------------------------------------
#define INF INT_MAX/2
int dp[1210][1210][3];
tuple<int,int,int> pre[1210][1210][3];
int ord[1210][1210][3];
int main() {
    cin >> N >> M >> S >> T;
    S += "#"; T += "#";

    rep(i, 0, N + 1) rep(j, 0, M + 1) rep(k, 0, 3) dp[i][j][k] = INF;
    rep(i, 0, N + 1) rep(j, 0, M + 1) rep(k, 0, 3) pre[i][j][k] = {-1, -1, -1};
    rep(i, 0, N + 1) rep(j, 0, M + 1) rep(k, 0, 3) ord[i][j][k] = -1;
    dp[0][0][0] = 0;

    rep(i, 0, N + 1) rep(j, 0, M + 1) rep(k, 0, 3){
        int d;

        // nothing : 3
        if (S[i] == T[j]) {
            if (dp[i][j][k] < dp[i + 1][j + 1][0]) {
                dp[i + 1][j + 1][0] = dp[i][j][k];
                pre[i + 1][j + 1][0] = {i, j, k};
                ord[i + 1][j + 1][0] = 3;
            }
        }

        // change : 0
        d = dp[i][j][k] + 5;
        if (d < dp[i + 1][j + 1][0]) {
            dp[i + 1][j + 1][0] = d;
            pre[i + 1][j + 1][0] = { i, j, k };
            ord[i + 1][j + 1][0] = 0;
        }
        

        // erase : 1
        d = dp[i][j][k] + 2;
        if (k != 1) d += 7;
        if (d < dp[i + 1][j][1]) {
            dp[i + 1][j][1] = d;
            pre[i + 1][j][1] = { i, j, k };
            ord[i + 1][j][1] = 1;
        }

        // insert : 2
        d = dp[i][j][k] + 2;
        if (k != 2) d += 7;
        if (d < dp[i][j + 1][2]) {
            dp[i][j + 1][2] = d;
            pre[i][j + 1][2] = { i, j, k };
            ord[i][j + 1][2] = 2;
        }
    }

    int ans = dp[N][M][0], kk = 0;
    rep(k, 1, 3) if (dp[N][M][k] < ans) ans = dp[N][M][k], kk = k;
    printf("%d\n", ans);

    vector<int> order;
    tuple<int, int, int> t = {N, M, kk};
    while (0 <= get<0>(t)) {
        int i, j, k;
        tie(i, j, k) = t;

        //printf("<%d %d %d>\n", i, j, k);

        order.push_back(ord[i][j][k]);
        t = pre[i][j][k];
    }
    order.pop_back();
    reverse(order.begin(), order.end());
    //for (int o : order) printf("%d ", o);
    //cout << endl;

    //return 0;

    string SS = "", TT = "";
    int i = 0, j = 0;
    for (int o : order) {
        if (o == 0) {
            assert(i <= N && j <= M);
            SS += S[i], i++;
            TT += T[j], j++;
        }
        else if(o == 1) {
            assert(i <= N);
            SS += S[i], i++;
            TT += "-";
        }
        else if (o == 2) {
            assert(j <= M);
            SS += "-";
            TT += T[j], j++;
        }
        else {
            assert(i <= N && j <= M);
            SS += S[i]; i++;
            TT += T[j]; j++;
        }
    }

    cout << SS << endl << TT << endl;
}