#include <bits/stdc++.h>

using namespace std;

int main() {
  int n, m;
  cin >> n >> m;

  string S, T;
  cin >> S >> T;

  vector<vector<int>> dp(n+1, vector<int>(m+1, 0));

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

  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= m; ++j) {
      if (S[i-1] == T[j-1])
        dp[i][j] = dp[i-1][j-1];
      else
        dp[i][j] = min({dp[i-1][j] + 1, dp[i][j-1] + 1, dp[i-1][j-1] + 1});
    }
  }

  cout << dp[n][m] << endl;
}