#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <map>
#include <stack>
#include <queue>
#include <set>
#include <cstring>

using namespace std;
// ascending order
#define vsort(v) sort(v.begin(), v.end())
// descending order
#define vsort_r(v) sort(v.begin(), v.end(), greater<int>())
#define vunique(v) unique(v.begin(), v.end())
#define mp make_pair
#define ts(x) to_string(x)
#define rep(i, a, b) for(int i = (int)a; i < (int)b; i++)
#define repm(i, a, b) for(int i = (int)a; i > (int)b; i--)
typedef long long ll;
typedef pair<int, int> P;
const ll INF = 1e18;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	int n, m;
	cin >> n >> m;
	string s, t;
	cin >> s >> t;
	ll dp[n + 1][m + 1];
	rep(i, 0, n + 1) rep(j, 0 , m + 1) dp[i][j] = INF;
	dp[0][0] = 0;
	rep(i, -1, n) {
		rep(j, -1, m) {
			if(i == -1 && j == -1) continue;
			if(s[i] != t[j]) dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + 1);
			else dp[i + 1][j + 1] = min(dp[i][j], dp[i + 1][j + 1]);
			if(i >= 0) dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j + 1] + 1);
			if(j >= 0) dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i + 1][j] + 1);
		}
	}

	cout << dp[n][m] << endl;
	
}