#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

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));
    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=1; i<=N; i++){
        for (int j=1; j<=M; j++){
            dp[i][j] = min(dp[i-1][j], dp[i][j-1]) + 1;
            dp[i][j] = min(dp[i][j], dp[i-1][j-1] + (S[i-1] == T[j-1] ? 0 : 1));
        }
    }

    cout << dp[N][M] << endl;

    return 0;
}