from types import GeneratorType

def bootstrap(f, stack=[]):
    def wrappedfunc(*args, **kwargs):
        if stack:
            return f(*args, **kwargs)
        to = f(*args, **kwargs)
        while True:
            if type(to) is GeneratorType:
                stack.append(to)
                to = next(to)
            else:
                stack.pop()
                if not stack:
                    break
                to = stack[-1].send(to)
        return to
    return wrappedfunc

def code(s):
    return ord(s)-ord("A")
def codeR(n):
    return chr(ord("A")+n)

@bootstrap
def dfs(n):
    while G[n]:
        v, s = G[n].pop()
        yield dfs(v)
        ans.append(s)
    yield

G = [[] for _ in range(26)]
for i in range(26):
    for j in range(26):
        G[i].append((j, codeR(j)+codeR(i)))

ans = []
dfs(0)

for a in ans:
    print(a)