s = list(input())
uni_s = set(s)
count = {}


if len(uni_s) != 7:
    print("Impossible")
else:
    for w in s:
        if w in count:
            count[w] += 1
        else:
            count[w] = 1

    for i, v in count.items():
        if v == 1:
            print(i)