text: #include <bits/stdc++.h>
  using namespace std;
  
  int friendPairing(int n)
  {
      int dp[n + 1];
      dp[0] = 1;
      dp[1] = 1;
      for (int i = 2; i <= n; i++)
      {
          dp[i] = dp[i - 1] + (i - 1) * (dp[i - 2]);
      }
      return dp[n];
  }
  
  int main()
  {
      int n;
      cin >> n;
      cout << friendPairing(n);
  }