#include <bits/stdc++.h> 
using namespace std;
int main(){
	int i=1,z,h=0;
	cin>>z;
	while(i<=z){
		h=h+i;
		i=i+2;
	}cout<<h;
}
/**************************************************************
	Problem: 1003
	User: sucongyi
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/