/*
TASK:necklace
LANG:C++
*/
#include<iostream>
#include<math.h>
using namespace std;
int a[60],b[60];
int main()
{
    int n,sa=0,sb=0,br=0;
    a[1]=1;
    cin>>n;
    for(int i=1;i<=n;i++)
    {   a[i]=1;
        b[i-1]=1;
        sa=sa+a[i];
        sb=sb+b[i];
        if(abs(sa-sb)%3==0)
        br++;
     }
     
     sa=0;
     sb=0;
     
     for(int i=1;i<=n;i++)
    {   a[i]=1;
        b[i]=0;
        sa=sa+a[i];
        sb=sb+b[i];
        if(abs(sa-sb)%3==0)
        br++;
     }
     sa=0;
     sb=0;
     for(int i=1;i<=n;i++)
    {   a[i]=1;
        b[i]=1;
        sa=sa+a[i];
        sb=sb+b[i];
        if(abs(sa-sb)%3==0)
        br++;
     }
     cout<<br<<"\n";
    //system("PAUSE");
    return 0;
    
}
