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

/**************************************************************
	Problem: 1694
	User: zzz
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/