N = int(input())

T = ["a"]*N
ans = []
for i in range(N):
    A = []
    for j in range(25):
        T[i] = chr(ord("a")+j)
        print("?", "".join(T))
        A.append(int(input()))
    T[i] = "a"
    if len(set(A)) == 1:
        ans.append("z")
    else:
        for j in range(25):
            S = sorted(list(set(A)))
            if A[j] == S[1]:
                ans.append(chr(ord("a")+j))
                break

print("".join(ans))