#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

const int INF = (1 << 30) - 1;
const ll INF64 = ((ll)1 << 62) - 1;
const double PI = 3.1415926535897932384626433832795;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { -1, 0, 1, 0 };

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

	int n, m;
	string s, t;
	cin >> n >> m >> s >> t;

	vector<vector<int>> dp(n + 1, vector<int>(m + 1, INF));
	dp[0][0] = 0;

	for (int i = 0; i <= n; i++) {
		dp[i][0] = i;
	}
	for (int j = 0; j <= m; j++) {
		dp[0][j] = j;
	}

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) {
			// 挿入 or 削除
			dp[i + 1][j + 1] = min(dp[i + 1][j], dp[i][j + 1]) + 1;
			// 未変更 or 変更
			dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + (s[i] != t[j]));
		}
	}

	cout << dp[n][m] << endl;
	return 0;
}