import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Scanner;


public class Y422 {
	Y422() throws IOException {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		int m = sc.nextInt();
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();

		int[][][][] dp = new int[n+1][m+1][2][2];
		int[][][][][] from = new int[n+1][m+1][2][2][];

		for (int i = 0; i <= S.length; i++) {
			for (int j = 0; j <= T.length; j++) {
				for (int a = 0; a < 2; a ++) {
					for (int b = 0; b < 2; b ++ ) {
						dp[i][j][a][b] = 100 * (n + m);
					}
				}
			}
		}
		
		dp[0][0][0][0] = 0;
				
		
		for (int i = 0; i < S.length; i++) {
			for (int j = 0; j < T.length; j++) {
				
				int change_cost = 5;
				if (S[i] == T[j]) change_cost = 0;

				int cost = change_cost + dp[i][j][0][0];
				{
					int[] tmp = { i, j, 0, 0 };
					dp[i+1][j+1][0][0] = cost;
					from[i+1][j+1][0][0] = tmp;
				}
				
				cost = change_cost + dp[i][j][0][1];
				if (cost < dp[i+1][j+1][0][0]) {
					int[] tmp = { i, j, 0, 1 };
					dp[i+1][j+1][0][0] = cost;
					from[i+1][j+1][0][0] = tmp;
				}
				
				cost = change_cost + dp[i][j][1][0];
				if (cost < dp[i+1][j+1][0][0]) {
					int[] tmp = { i, j, 1, 0 };
					dp[i+1][j+1][0][0] = cost;
					from[i+1][j+1][0][0] = tmp;
				}
				
				
				cost = 9 + dp[i+1][j][0][0];
				{
					int[] tmp = { i+1, j, 0, 0 };
					dp[i+1][j+1][1][0] = cost;
					from[i+1][j+1][1][0] = tmp;
				}
				
				cost = 2 + dp[i+1][j][1][0];
				if (cost < dp[i+1][j+1][1][0]) {
					int[] tmp = { i+1, j, 1, 0 };
					dp[i+1][j+1][1][0] = cost;
					from[i+1][j+1][1][0] = tmp;
				}

				cost = 9 + dp[i+1][j][0][1];
				if (cost < dp[i+1][j+1][1][0]) {
					int[] tmp = { i+1, j, 0, 1 };
					dp[i+1][j+1][1][0] = cost;
					from[i+1][j+1][1][0] = tmp;
				}
				
				
				cost = 9 + dp[i][j+1][0][0];
				{
					int[] tmp = { i, j+1, 0, 0 };
					dp[i+1][j+1][0][1] = cost;
					from[i+1][j+1][0][1] = tmp;
				}
				
				cost = 9 + dp[i][j+1][1][0];
				if (cost < dp[i+1][j+1][0][1]) {
					int[] tmp = { i, j+1, 1, 0 };
					dp[i+1][j+1][0][1] = cost;
					from[i+1][j+1][0][1] = tmp;
				}
				
				cost = 2 + dp[i][j+1][0][1];
				if (cost < dp[i+1][j+1][0][1]) {
					int[] tmp = { i, j+1, 0, 1 };
					dp[i+1][j+1][0][1] = cost;
					from[i+1][j+1][0][1] = tmp;
				}
			}
		}
		
		
		int cost = 100 * (n + m);
		int[] state = null;
		for (int a = 0; a < 2; a++) {
			for (int b = 0; b < 2; b++) {
				if (cost > dp[S.length][T.length][a][b]) {
					cost = dp[S.length][T.length][a][b];
					int[] tmp = {S.length, T.length, a, b};
					state = tmp;
				}
			}
		}
		
		
		char[] S_ans = new char[n+m];
		char[] T_ans = new char[n+m];
		int len = 0;
		
		while (state[0] != 0 || state[0] != 0) {
			int[] next = from[state[0]][state[1]][state[2]][state[3]];

			if (state[2] == 1) {
				S_ans[len] = '-';
			} else {
				S_ans[len] = S[next[0]];
			}
			if (state[3] == 1) {
				T_ans[len] = '-';
			} else {
				T_ans[len] = T[next[1]];
			}
			len++;
			state = next;
		}

		OutputStream os = new BufferedOutputStream(System.out);
		
		os.write(Integer.toString(cost).getBytes());
		os.write('\n');

		for (int i = len - 1; i >= 0; i--) {
			os.write(S_ans[i]);
		}
		os.write('\n');

		for (int i = len - 1; i >= 0; i--) {
			os.write(T_ans[i]);
		}
		os.write('\n');
	
		os.flush();
	}
	public static void main(String argv[]) throws IOException {
		new Y422();
	}
}