#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,s=0;
	cin>>n;
	while(1<=n){
		s=s+n;
		n=n-2;
	}
	cout<<s;
return 0;
}
/**************************************************************
	Problem: 1003
	User: houshanglin
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/