[cpp]
#include
long long a[21];
int main()
{
int n,i;
a[2]=1;
a[3]=2;
for(i=4;i<=20;i++)
a[i]=(i-1)*(a[i-1]+a[i-2]);
while(scanf("%d",&n)!=EOF)
printf("%lld\n",a[n]);
}