#include<bits/stdc++.h>
using namespace std;
int D(int n){
	if(n==1) return 0;
	else if(n==2) return 1;
	else return (n-1)*( D(n-1)+D(n-2)); 
}
int main(){
	int x;
	cin>>x;
	cout<<D(x); 
	return 0;
}

/**************************************************************
	Problem: 1694
	User: houshanglin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/