#include <bits/stdc++.h>
#include <math.h>
using namespace std;
using ll = long long;
using vll = vector<ll>;
using vvll = vector<vll>;
using vpl = vector<pair<ll, ll>>;
using pll = pair<ll, ll>;
#define rep(i, k, n) for(ll i = k; i < n; i++)
#define pb push_back
#define mp make_pair
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

ll n, m;
string s, t;
const ll INF = 10000000000;
vvll dp(1010, vll(1010, INF));

int main(){
    cin >> n >> m >> s >> t;

    dp[0][0] = 0;

    rep(i, -1, n){
        rep(j, -1, m){
            if(i == -1 && j == -1) continue;

            if(i == -1){
                chmin(dp[i+1][j+1], dp[i+1][j] + 1);
                continue;
            }

            if(j == -1){
                chmin(dp[i+1][j+1], dp[i][j+1] + 1);
                continue;
            }

            if(s[i] == t[j]) chmin(dp[i+1][j+1], dp[i][j]);

            //変更
            chmin(dp[i+1][j+1], dp[i][j] + 1);

            //削除
            chmin(dp[i+1][j+1], dp[i][j+1] + 1);

            //挿入
            chmin(dp[i+1][j+1], dp[i+1][j] + 1);
        }
    }

    cout << dp[n][m] << endl;
}