ALPHA = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
SIGMA = 26

answer = []

for i in range(SIGMA):
    for j in range(SIGMA - 1, i + 1, -1):
        answer.append(ALPHA[i] + ALPHA[j])
        answer.append(ALPHA[j] + ALPHA[i])
    if i < SIGMA - 1:
        answer.append(ALPHA[i] + ALPHA[i + 1])

for i in range(SIGMA - 1, 0, -1):
    answer.append(ALPHA[i] + ALPHA[i - 1])

print(*answer, sep="\n")