#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <set>
using namespace std;

int main(){
	int n, m;
	cin >> n >> m;
	string s,t;
	cin >> s >> t;
	vector<vector<int>> dp(n+1, vector<int>(m+1, 0));
	for(int i=0; i<n; i++){
		dp[i][0] = i;
	}
	for(int i=0; i<m; i++){
		dp[0][i] = i;
	}
	for(int i=1; i<=n; i++){
		for(int j=1; j<=m; j++){
			dp[i][j] = min({dp[i-1][j] + 1, dp[i][j-1] + 1, dp[i-1][j-1] + (s[i-1]!=t[j-1]?1:0)});
		}
	}
	cout << dp[n][m] << endl;
	return 0;
}