#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)




int N, M; string S, T;
//-----------------------------------------------------------------------------------
#define INF INT_MAX/2
int dp[1010][1010];
int main() {
    cin >> N >> M >> S >> T;

    rep(i, 0, 1010) rep(j, 0, 1010) dp[i][j] = INF;
    dp[0][0] = 0;

    rep(i, 0, N + 1) rep(j, 0, M + 1) {
        if (i == N && j == M) continue;
        if (i == N) dp[i][j + 1] = min(dp[i][j + 1], dp[i][j] + 1);
        else if (j == M) dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + 1);
        else {
            // nothing
            if (S[i] == T[j]) {
                dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j]);
            }

            // change
            dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + 1);

            // erase
            dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + 1);

            // insert
            dp[i][j + 1] = min(dp[i][j + 1], dp[i][j] + 1);
        }
    }

    printf("%d\n", dp[N][M]);
}