#include<iostream>
#include<fstream>
#include<sstream>
#include<string>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<stack>
#include<queue>
#include<set>
#include<map>
#include<vector>
#include<list>
#include<algorithm>
#include<utility>
#include<complex>
#include<functional>
using namespace std;


#define input_init stringstream ss; string strtoken, token; istringstream is
#define input_line  getline(cin, strtoken);is.str(strtoken);is.clear(istringstream::goodbit)
#define input_token(num) ss.str(""); ss.clear(stringstream::goodbit); getline(is, token, ','); ss << token; ss >> num

int dp[1001][1001];
int ii[1001][1001];
int jj[1001][1001];
int main(void){
	int n,m;
	string s;
	string t;
	cin >> n>>m >> s >> t;
	dp[0][0] = 1;
	ii[0][0] = jj[0][0] = -1;
	for (int i = 0; i < n; i++){
		for (int j = 0; j < m; j++){
			if (s[i] == t[j]){
				dp[i + 1][j + 1] = dp[i][j] + 1;
				ii[i + 1][j + 1] = i;
				jj[i + 1][j + 1] = j;

			}
			else{
				if (dp[i + 1][j] > dp[i][j + 1]){
					dp[i + 1][j + 1] = dp[i + 1][j];
					ii[i + 1][j + 1] = ii[i+1][j];
					jj[i + 1][j + 1] = jj[i+1][j];
				}
				else{
					dp[i + 1][j + 1] = dp[i][j+1];
					ii[i + 1][j + 1] = ii[i][j+1];
					jj[i + 1][j + 1] = jj[i][j+1];
				}
			}
		}
	}
	string com;
	int x=n, y=m;
	while (ii[x][y] >= 0){
		com = s[ii[x][y]]+com;
		int t = x;
		x = ii[t][y];
		y = jj[t][y];
	}
	//cout << com << endl;
	int len = (int)com.size();
	int res = 0;
	int nn = 0;
	for (int i = 0; i < m; i++){
		//cout << s << " " << t << " " << i <<" "<<nn<< endl;;
		if (nn >= len){
			res++;
		}
		else if (com[nn] == s[i] && com[nn] == t[i])nn++;
		else if (s[i] == t[i])continue;
		else if (com[nn] == s[i]){
			s.insert(i, t.substr(i, 1));
			res++;
		}
		else if (com[nn] == t[i]){
			s.erase(i, 1);
			i--;
			res++;
		}
		else{
			s[i] = t[i];
			res++;
		}
	}
	cout << res << endl;
	return(0);
}