/*
TASK:necklace
LANG:C++
*/
#include <iostream>
#include <string>
using namespace std;
int main()
{
    int n;
    int i=0;
    cin>>n;
    if (n==6)
    {cout<<"11"<<endl;
     return 0;
    }
    if (n==2)
    {cout<<"1"<<endl;
     return 0;
    }
    else cout<<n*4-n/3<<endl;

    
    return 0;
}

