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

#define MAX 1100
#define INF 1<<29

template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

int n, m;
string S, T;

int dp[MAX][MAX];

int main() {
  while (cin >> n >> m) {
    cin >> S >> T;
    S += "?"; T += "?";
    for (int i = 0; i < MAX; ++i)
      for (int j = 0; j < MAX; ++j)
	dp[i][j] = INF;
    dp[0][0] = 0;
    for (int i = 0; i <= n; ++i) {
      for (int j = 0; j <= m; ++j) {
	if (S[i] == T[j])
	  chmin(dp[i+1][j+1], dp[i][j]);
	else
	  chmin(dp[i+1][j+1], dp[i][j] + 1);
	chmin(dp[i+1][j], dp[i][j] + 1);
	chmin(dp[i][j+1], dp[i][j] + 1);
      }
    }
    cout << dp[n][m] << endl;
  }
}