def del_string(string):
    dic = {}
    for i in string:
        if i not in dic.keys():
            dic[i] = string.count(i)
    count = sorted(dic.values())[0]
    for key, value in dic.items():
        if value == count:
            string = string.replace(key, '')
    print(string)


while 1:
    try:
        s = input()
        del_string(s)
    except:
        break