#include<bits/stdc++.h>
using namespace std;
int main(){
	int i=1,h=0,n;
	cin>>n;
	while(i<=n){
		h=i+h;
		i=i+2;
	}
	cout<<h;
}
/**************************************************************
	Problem: 1003
	User: huanglingkai
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/