package N4xx;

import java.util.*;

public class N422 {
	public static void main(String[] args) {
		new N422().solver();
	}

	int N, M;
	String S, T;
	int[][][] dp;

	void solver() {
		Scanner sc = new Scanner(System.in);
		N = sc.nextInt();
		M = sc.nextInt();
		S = sc.next();
		T = sc.next();
		dp = new int[1300][1300][3];
		for (int i = 0; i < dp.length; i++) {
			for (int j = 0; j < dp[i].length; j++) {
				for (int k = 0; k < dp[i][j].length; j++) {
					dp[i][j][i] = -1;
				}
			}
		}
		System.out.println(dpdp(0, 0, 0));
		System.out.println(RS + "\n" + RT);
	}

	String RS = "";
	String RT = "";

	int dpdp(int s, int t, int st) {
		if (s == N && t == M)
			return 0;
		int ret = dp[s][t][st];
		if (ret != -1)
			return ret;
		ret = 10101010;
		if (s < N && t < M)
			ret = Math.min(ret, dpdp(s + 1, t + 1, 0) + ((S.charAt(s) == T.charAt(t) ? 0 : 5)));
		if (s < N)
			ret = Math.min(ret, st == 2 ? 2 : 9 + dpdp(s + 1, t, 2));
		if (t < M)
			ret = Math.min(ret, st == 1 ? 2 : 9 + dpdp(s, t + 1, 1));
		return dp[s][t][st] = ret;
	}

	void dfs(int s, int t, int st) {
		if (s == N && t == M)
			return;
		int ret = dp[s][t][st];

		if (s < N && t < M && ret == (dpdp(s + 1, t + 1, 0) + S.charAt(s) == T.charAt(t) ? 0 : 5)) {
			RS += S.charAt(s);
			RT += T.charAt(t);
			dfs(s + 1, t + 1, 0);
		} else if (s < N && ret == (dpdp(s + 1, t, 2) + st == 2 ? 2 : 9)) {
			RS += S.charAt(s);
			RT = "-";
			dfs(s + 1, t, 2);
		} else if (t < M && ret == (dpdp(s, t + 2, 1) + st == 1 ? 2 : 9)) {
			RS += "-";
			RT += T.charAt(t);
			dfs(s, t + 1, 1);
		}
	}
}