ans = []
def dfs(c):
	ans.append((c, c))
	for nc in range(c + 2, 26):
		ans.append((c, nc))
		ans.append((nc, c))
	
	if c != 25:
		ans.append((c, c + 1))
		dfs(c + 1)
		ans.append((c + 1, c))
dfs(0)

for c1, c2 in ans:
	print(chr(ord('A') + c1) + chr(ord('A') + c2))