#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    cout<<(n+1)*((n+1)*0.5)*0.5;
}
/**************************************************************
	Problem: 1003
	User: liyunshuo
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/