import sys

sample = "abcdefghijklm"

def main():
    S = input()
    if is_include_invalid_char(S):
        print("Impossible")
        sys.exit()

    if len(set(S)) == 13:
        for s in list(sample):
            print(s)
    elif len(set(S)) == 12:
        for x, y in zip(list(sample), sorted(list(set(S)))):
            if not x == y:
                print(x)
                sys.exit()
        print(sample[-1])
    else:
        print("Impossible")

def is_include_invalid_char(values):
    for s in list(values):
        if not s in sample:
            return True
    return False

if __name__ == '__main__':
    main()