#include<bits/stdc++.h>
using namespace std;
int n;
int xinfeng(int n){
	if(n==1)return 0;
	else if(n==2)return 1;
	else return (n-1)*(xinfeng(n-1)+xinfeng(n-2));
}
int main(){
	cin>>n;
	cout<<xinfeng(n);
    return 0;
}
/**************************************************************
	Problem: 1694
	User: admin
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/