#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,h=0,i=1;
	cin>>n;
	while(i<=n){
		h=h+i;
		i=i+2;
	} 
	cout<<h;
	return 0;
} 
/**************************************************************
	Problem: 1003
	User: fuhoubin
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/