#include <iostream>
#include <vector>
#include <string>
using namespace std;

int main(){
    int n, m;
    cin >> n >> m;
    string s, t;
    cin >> s;
    cin >> t;
    vector<vector<int>> memo(n+1, vector<int>(m+1, 1001001001));
    memo[0][0] = 0;
    for(int i = 1; i <= n; i++) memo[i][0] = i;
    for(int j = 1; j <= m; j++) memo[0][j] = j;

    for(int i = 0; i <= n; i++){
        for(int j = 0; j <= m; j++){
            if(i > 0 && j > 0){
                if(memo[i][j] > memo[i-1][j-1] +
                ((s[i-1] == t[j-1]) ? 0 : 1)){
                    memo[i][j] = memo[i-1][j-1] +
                    ((s[i-1] == t[j-1]) ? 0 : 1);
                }
            }
            if(i > 0 && memo[i][j] > memo[i-1][j]+1){
                memo[i][j] = memo[i-1][j]+1;
            }
            if(j > 0 && memo[i][j] > memo[i][j-1]+1){
                memo[i][j] = memo[i][j-1]+1;
            }
        }
    }
    cout << memo[n][m] << endl;
    return 0;
}