include<bits/stdc++.h>

using namespace std;
namespace{
template<typename t="">
inline void read(T &s){
T f=1;s=0;char ch=getchar();
for(;!isdigit(ch);ch=getchar()) if(ch=='-') f=-1;
for(;isdigit(ch);ch=getchar()) s=(s<<1)+(s<<3)+(ch^48);
s=f;
}
}
#define ll long long
int n;
ll f[25];
int main(){
read(n);
f[2]=1;
for(int i=3;i<=n;++i){
f[i]=(i-1)(f[i-1]+f[i-2]);
}
cout << f[n];
return 0;
}</typename>