#include<bits/stdc++.h>
using namespace std;
void combination(int pos,char letter)
{
    if(pos==3)
    {

        return;
    }
    if(pos==0)
    {
        combination(pos+1,'a');
        combination(pos+1,'b');
        combination(pos+1,'c');
    }
    else
    {
        if(letter=='a')
        {
            combination(pos+1,'b');
            combination(pos+1,'c');
        }
        else if(letter=='b')
        {
            combination(pos+1,'a');
            combination(pos+1,'c');
        }
        else
        {
            combination(pos+1,'a');
            combination(pos+1,'b');
        }

    }
}
int main()
{
    combination(1,'a');
    return 0;
}