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

/**************************************************************
	Problem: 1003
	User: ljl2
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/