#include<bits/stdc++.h>
using namespace std;
int a,ans;
int main(){
	  cin>>a;
	  for(int i=1;i<=a;i+=2){
	  	ans+=i;
	  }        
	  cout<<ans;                    
	return 0;
}
/**************************************************************
	Problem: 1003
	User: chenjingqi
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/