#include <iostream>
#include <algorithm>

int N, M;
std::string S, T;
int dp[1001][1001];

int main(){
    std::cin >> N >> M;
    std::cin >> S >> T;

    for(int i=1;i<=N;i++){
        dp[i][0] = i;
    }

    for(int i=1;i<=M;i++){
        dp[0][i] = i;
    }

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

    std::cout << dp[N][M] << std::endl;
}