_ = input()
print("? aa")
s = set(["aa"])

while True:
    x = input().split()[1]
    if "WIN" in x:
        break
    if x[0] != "a" or x in s:
        _ = input()
        break
    t = x[-1] + "a"
    s.add(x)
    s.add(t)
    print("?", t)