#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <queue>
#include <stack>
#include <set>
#include <map>

#define repd(i,a,b) for (int i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
typedef long long ll;

using namespace std;


int inputValue(){
    int a;
    cin >> a;
    return a;
};

template <typename T>
void output(T a, int precision) {
    if(precision > 0){
        cout << setprecision(precision)  << a << "\n";
    }
    else{
        cout << a << "\n";
    }
}

int main() {
    
    // source code
    int n = inputValue();
    int m = inputValue();
    
    string s, t;
    cin >> s >> t;
    
    vector<vector<int>> dp(n, vector<int> (m, 0));
    
    rep(i, n){
        dp[i][0] = i;
    }
    rep(j, m){
        dp[0][j] = j;
    }
    
    repd(i, 1, n){
        repd(j, 1, m){
            int cost = 1;
            if (s[i] == t[j]) {
                cost = 0;
            }
            
            dp[i][j] = min(dp[i - 1][j] + 1, min(dp[i][j - 1] + 1, dp[i - 1][j - 1] + cost));
        }
    }
    
    output(dp[n - 1][m - 1], 0);
    
    return 0;
}