import bisect
import math
import string
import sys
from itertools import accumulate
from math import isqrt, inf
from typing import List, Tuple

sys.setrecursionlimit(10 ** 6)

MOD = 998244353

int1 = lambda x: int(x) - 1
input = lambda: sys.stdin.readline().rstrip('\n')
ii = lambda: int(input())
vi = lambda: list(map(int, input().split()))
vi1 = lambda: list(map(int1, input().split()))


def dbg(*args, **kwargs):
    print(*(repr(arg) for arg in args), *(f'{k}: {repr(v)}' for k, v in kwargs.items()),
          sep='; ', file=sys.stderr, flush=True)


def main():
    s = set()

    def dfs(x):
        for i in string.ascii_uppercase:
            if x + i not in s:
                if x == i:
                    s.add(x + i)
                    print(x + i)
                    continue
                s.add(x + i)
                s.add(i + x)
                print(x + i)
                dfs(i)
                print(i + x)

    dfs('A')


def _start():
    if (ret := main()) is not None:
        print(*ret) if isinstance(ret, List) or isinstance(ret, Tuple) else print(ret)


if __name__ == '__main__':
    _start()