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

cout<<q<<endl; 
	return 0;
}
/**************************************************************
	Problem: 1003
	User: czr
	Language: C++
	Result: Accepted
	Time:17 ms
	Memory:2072 kb
****************************************************************/