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




#define INF INT_MAX/2
int N, M; string S, T;
//-----------------------------------------------------------------------------------
int dp[1010][1010];
int rec(int i, int j) {
    if (0 <= dp[i][j]) return dp[i][j];

    if (i == 0 && j == 0) return dp[i][j] = 0;

    int res = INF;
    if (0 < i) res = min(res, rec(i - 1, j) + 1);
    if (0 < j) res = min(res, rec(i, j - 1) + 1);

    if (0 < i && 0 < j) {
        if (S[i - 1] == T[j - 1]) res = min(res, rec(i - 1, j - 1));
        else res = min(res, rec(i - 1, j - 1) + 1);
    }

    return dp[i][j] = res;
}
//-----------------------------------------------------------------------------------
int main() {
    cin >> N >> M >> S >> T;
    rep(i, 0, 1010) rep(j, 0, 1010) dp[i][j] = -1;
    cout << rec(N, M) << endl;
}