#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>
//---------------------------
using namespace std;
//---------------------------
#define REP(i,n) for(int i = 0; i < (n); i++)
#define P(x) cout << (x) << "\n"
//---------------------------

int main(){


  int n;cin >> n;
  if (n == 1) {
    P(1);
  }else{
  vector<int> v(n+1);
  v[0]=0;
  v[1]=1;
  for (int i = 2; i < n+1; i++) {
    v[i] = i * v[i-1] + v[i-2];
  }

  cout << v[n] - v[n-2] << "\n";
}
  return 0;
}