/*
TASK:necklace
LANG:C++
*/

#include<iostream>
#include<math.h>
using namespace std;
long n,m,i,j,k,l,br,a[101],p,q,d;
int main()
{ cin>>n;
  a[1]=1;
  if(n==2 || n==3) br=1;
  if(n==4) br=3;
  if(n==5) br=4;
  if(n==6) br=11;
  if(n>6)
   {
	 for(i=2; i<=n; i=i+2)
	  br++;
	 if(n%3==0)
	   br=br+n/3;
	 for(i=2; i<=n; i++)
	  for(k=2; k<=i; k++)
	   { for(j=2; j<=n; j++)
		  { a[i]=1;
			if(i%2==0) q++;
			else p++;
		  }
		  d=abs(p-q);
		  if(d%3==0) br++;
	   }
   }
   cout<<br;
   cout<<endl;
return 0;
}