#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,s=1,h=0;
	cin>>n;
	while(s<=n){
	h=h+s;
	s+=2;
		}
	cout<<h;



	
}
/**************************************************************
	Problem: 1003
	User: zhuangwenya
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/