#include <iostream>
using namespace std;

void a(char c, bool b)
{
    for(char i='A';i<c;i++)
        cout << i;

    if(b)
        cout << (char)(c+' ');
    else
        cout << c;

    cout << endl;

    if(!b || c!='A')
        a(c-b, !b);
}

int main()
{
    a('Z', 0);
}