#include<bits/stdc++.h>
using namespace std;
int n;
int ss(int x){
	if(x==1) return 0;
	if(x==2) return 1;
	return (x-1)*(ss(x-1)+ss(x-2));
}
int main(){
	cin>>n;
	cout<<ss(n);
return 0;}
/**************************************************************
	Problem: 1694
	User: fzy001
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/