#include <iostream>
#include <cstring>
#include <tuple>
using namespace std;

int n, m;
string S, T;

enum state {
    normal,
    del,
    insert
};

typedef tuple<int, int, state> pos;

int dp[1300][1300][5];
pos nxt[1300][1300][5];

int solve(int, int, state);
void update(int& res, pos& p, int a, int b, state s, int add) {
    int cost = solve(a, b, s) + add;
    if(cost < res) {
        res = cost;
        p = make_tuple(a, b, s);
    }
}

int solve(int a, int b, state s) {
    if(a == n && b == m) {
        return 0;
    }
    if(a == n) {
        return 9 + 2 * (m - b - 1);
    }
    if(b == m) {
        return 9 + 2 * (n - a - 1);
    }
    if(dp[a][b][s] != -1)return dp[a][b][s];

    int res = 1 << 25;
    pos np;
    
    // 変更してみる
    update(res, np, a + 1, b + 1, normal, (S[a] == T[b]) ? 0 : 5);
    // 挿入してみる
    update(res, np, a, b + 1, insert, (s == insert) ? 2 : 9);
    // 削除してみる
    update(res, np, a + 1, b, del, (s == del) ? 2 : 9);

    nxt[a][b][s] = np;
    return dp[a][b][s] = res;
}

string accS, accT;

void dfs(int a, int b, state s) {
    if(a == n && b == m) {
        return;
    }
    if(a == n) {
        accS += string(m - b, '-');
        accT += T.substr(b);
        return;
    }
    if(b == m) {
        accS += S.substr(a);
        accT += string(n - a, '-');
        return;
    }

    pos np = nxt[a][b][s];
    int na = get<0>(np), nb = get<1>(np);
    state ns = get<2>(np);

    switch (ns) {
    case normal:
        accS += S[a];
        accT += T[b];
        break;
    case del:
        accS += S[a];
        accT += '-';
        break;
    case insert:
        accS += '-';
        accT += T[b];
        break;
    }

    dfs(na, nb, ns);
}

int main() {
    memset(dp, -1, sizeof(dp));

    cin >> n >> m;
    cin >> S >> T;

    cout << solve(0, 0, normal) << endl;

    dfs(0, 0, normal);
    cout << accS << endl;
    cout << accT << endl;

    return 0;
}