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

/**************************************************************
	Problem: 1003
	User: ct001
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/