#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int N,M;
    string S,T;
    cin >> N >> M >> S >> T;
    int dp[N+1][M+1] = {};
    rep(i,0,N+1)dp[i][0] = i;
    rep(i,0,M+1)dp[0][i] = i;

    rep(i,1,N+1)rep(j,1,M+1){
        int cost = !(S[i-1] == T[j-1]);
        dp[i][j] = min({
            dp[i-1][j] + 1,
            dp[i][j-1] + 1,
            dp[i-1][j-1] + cost
        });
    }
    cout << dp[N][M] << endl;
}