#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
const int INF = 1 << 30;
const int MOD = 1e9 + 7;

template<class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

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

int main() {
  int n, m;
  string S, T;
  cin >> n >> m >> S >> T;
  vector<vector<int>> dp(1001, vector<int>(1001, INF));
  dp[0][0] = 0;
  for (int i = -1; i < n; i++) {
    for (int j = -1; j < m; j++) {
      if (i == -1 && j == -1) continue;
      if (i >= 0 && j >= 0) {
        if (S[i] == T[j]) {
          dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j]);
        }
        else {
          dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + 1);
        } 
      }
      if (i >= 0) dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j + 1] + 1);
      if (j >= 0) dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i + 1][j] + 1);
    }
  }
  cout << dp[n][m] << endl;
  return 0;
}