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


	return 0;
}

/**************************************************************
	Problem: 1003
	User: zy002
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/