#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < (int)n; ++i)
using ll = long long;
const ll INF = 1LL<<60;

template<class T> inline bool chmin(T& a, T b) {if (a > b) {a = b; return true;} return false;}
template<class T> inline bool chmax(T& a, T b) {if (a < b) {a = b; return true;} return false;}

int main() {
    int n, m; cin >> n >> m;
    string S, T; cin >> S >> T;

    vector<vector<ll>> dp(S.size()+1, vector<ll>(T.size()+1, INF));
    rep(i, S.size()+1) dp[i][0] = i;
    rep(i, T.size()+1) dp[0][i] = i;

    rep(i, S.size()) rep(j, T.size()) {
        if (S[i] == T[j]) chmin(dp[i+1][j+1], dp[i][j]); // copy
        chmin(dp[i+1][j+1], dp[i][j] + 1); // replace
        chmin(dp[i+1][j+1], dp[i][j+1] + 1); // delete
        chmin(dp[i+1][j+1], dp[i+1][j] + 1); // insert
    }

    cout << dp[S.size()][T.size()] << endl;

    return 0;
}