/* -*- coding: utf-8 -*-
 *
 * 225.cc: No.225 文字列変更(medium) - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 1000;
const int MAX_M = 1000;

const int INF = 1 << 30;

/* typedef */

/* global variables */

int dp[MAX_N + 1][MAX_M + 1];

/* subroutines */

/* main */

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

  for (int i = 0; i <= n; i++)
    for (int j = 0; j <= m; j++) dp[i][j] = INF;
  dp[0][0] = 0;

  for (int i = 0; i <= n; i++)
    for (int j = 0; j <= m; j++)
      if (dp[i][j] < INF) {
	if (i < n && j < m) {
	  int d = dp[i][j] + ((s[i] == t[j]) ? 0 : 1);
	  if (dp[i + 1][j + 1] > d) dp[i + 1][j + 1] = d;
	}

	if (i < n) {
	  int d = dp[i][j] + 1;
	  if (dp[i + 1][j] > d) dp[i + 1][j] = d;
	}
	if (j < m) {
	  int d = dp[i][j] + 1;
	  if (dp[i][j + 1] > d) dp[i][j + 1] = d;
	}
      }

  printf("%d\n", dp[n][m]);
  return 0;
}