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

/**************************************************************
	Problem: 1110
	User: liujinhao
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/