希丰展？使md
by OldVagrant @ 2021-12-27 10:56:53
```c
#include<iostream>
using namespace std;
int main(){
unsigned long long x;
cin>>x;
cout<<x*(x-1)/2*(x-2)/3*(x-3)/4<<endl;
return 0;
}
```
by nemo2010 @ 2022-07-21 18:50:41