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


/**************************************************************
	Problem: 1003
	User: 15159808820
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/