#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, m;
    string s, t;
    cin >> n >> m >> s >> t;
    vector<vector<int>> dp(n + 1, vector<int>(m + 1, INF));
    dp[0][0] = 0;
    for(int i = 0; i <= n; ++i){
        for(int j = 0; j <= m; ++j){
            if(j - 1 >= 0){
                chmin(dp[i][j], dp[i][j - 1] + 1);
            }
            if(i - 1 >= 0){
                chmin(dp[i][j], dp[i - 1][j] + 1);
            }
            if(i - 1 >= 0 && j - 1 >= 0){
                chmin(dp[i][j], dp[i - 1][j - 1] + (s[i - 1] != t[j - 1]));
            }
        }
    }
    cout << dp[n][m] << endl;

    return 0;
}