#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
using namespace std;
int f[25],n;
int main()
{
	scanf("%d",&n);
	f[1]=0;f[2]=1;f[3]=2;
	if(n==1||n==2||n==3)
	{
		printf("%d",f[n]);
		return 0;
	}
	for(int i=4;i<=n;i++)
	{
		f[i]=(i-1)*(f[i-1]+f[i-2]);
	}
	printf("%d",f[n]);
	return 0;
 }