#include<bits/stdc++.h>
template<typename T> inline bool chmax(T &a, const T &b){if(a < b){a = b; return true;}return false;}
using namespace std;
using ll = long long;

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