#include<bits/stdc++.h>
using namespace std;
int main(){
	int n=0,c=0,b=1;
	cin>>n;
	while(b<=n){
		c=b+c;
		b=b+2;	
		}
		   
    cout<<c;
}
/**************************************************************
	Problem: 1110
	User: lvrenxiang
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/