#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

int main() {
	int n, m;
	string S, T;

	cin >> n >> m >> S >> T;

	vector<vector<int>> dp(n + 1);
	for (vector<int>& t : dp) {
		t.resize(m + 1);
		fill(t.begin(), t.end(), 0);
	}

	for (int i = 0; i < n + 1; ++i) {
		dp[i][0] = i;
	}
	for (int i = 0; i < m + 1; ++i) {
		dp[0][i] = i;
	}
	
	for (int i = 1; i < n + 1; ++i) {
		for (int j = 1; j < m + 1; ++j) {
			int dist1 = dp[i - 1][j - 1] + ((S[i - 1] == T[j - 1]) ? 0 : 1);
			int dist2 = dp[i - 1][j] + 1;
			int dist3 = dp[i][j - 1] + 1;
			dp[i][j] = min(dist1, min(dist2, dist3));
		}
	}

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