11150 - Cola

Just scribe a little on paper, you would get it. ;)

//
//  main.cpp
//  11150 - Cola
//
//  Created by Panks on 29/05/12.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#include <iostream>
using namespace std;
int main (int argc, const char * argv[])
{

    int a, tmp;
    while (cin>>a) {
        if (a==1||a==0) {
            cout<<a<<endl;
            continue;
        }
        tmp=a;
        a=a+a/2;
        a=a-a%3;
        cout<<tmp+(a/3)<<endl;
    }
    return 0;
}