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

/**************************************************************
	Problem: 1003
	User: binzicheng1
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/