#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,b=1,c=0;
	cin>>n;
	while(b<=n){
		c=b+c;
		b=b+2;
		
	}
	cout<<c;
	}  
/**************************************************************
	Problem: 1003
	User: lvrenxiang
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/