#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c=0;
	cin>>a;
	for(b=1;b<=a;b+=2){
		c=c+b;
	}
	cout<<c;
}
/**************************************************************
	Problem: 1110
	User: zengyixuan
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/