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