#include <iostream>
#include <cstring>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cassert>
using namespace std;
const int INF = 1 << 28;

// 0:default, 1:delete, 2:insert
int dp[1300][1300][3];
// 0:replace, 1:delete: 2:insert
int pre[1300][1300][3];


int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int n, m;
	cin >> n >> m;

	string S, T;
	cin >> S >> T;

	fill((int*)begin(pre), (int*)end(pre), -1);
	fill((int*)begin(dp), (int*)end(dp), INF);
	dp[0][0][0] = 0;
	for(int i = 0; i <= n; i++) {
		for(int j = 0; j <= m; j++) {
			for(int k = 0; k < 3; k++) {
				if(dp[i][j][k] == INF) continue;

				int v = dp[i][j][k], nv;
				// replace
				if(i < n && j < m) {
					nv = v + ((S[i] == T[j]) ? 0 : 5);
					if(dp[i + 1][j + 1][0] > nv) {
						dp[i + 1][j + 1][0] = nv;
						pre[i + 1][j + 1][0] = k;
					}
				}
				// delete
				if(i < n) {
					nv = v + ((k == 1) ? 2 : 9);
					if(dp[i + 1][j][1] > nv) {
						dp[i + 1][j][1] = nv;
						pre[i + 1][j][1] = k;
					}
				}
				// insert
				if(j < m) {
					nv = v + ((k == 2) ? 2 : 9);
					if(dp[i][j + 1][2] > nv) {
						dp[i][j + 1][2] = nv;
						pre[i][j + 1][2] = k;
					}
				}
			}
		}
	}

	int  mink = -1, minc = INF;
	for(int k = 0; k < 3; k++) {
		if(dp[n][m][k] < minc) {
			minc = dp[n][m][k];
			mink = k;
		}
	}
	assert(mink != -1);

	cout << minc << endl;
	int ni = n, nj = m, nk = mink;
	string s, t;
	while(true) {
		if(nk == 0) {
			nk = pre[ni][nj][nk];
			s = S[ni - 1] + s;
			t = T[nj - 1] + t;
			ni--, nj--;

		}
		else if(nk == 1) {
			nk = pre[ni][nj][nk];
			s = S[ni - 1] + s;
			t = '-' + t;
			ni--;
		}
		else {
			nk = pre[ni][nj][nk];
			s = '-' + s;
			t = T[nj - 1] + t;
			nj--;
		}
		if(ni == 0 && nj == 0 && nk == 0);
	}
	cout << s << endl;
	cout << t << endl;
}