def func():

    s = input()

    resdict = {}
    for i in s:
        resdict[i] = resdict.get(i, 0) + 1

    sorted_resdict = sorted(resdict.items(), key=lambda item : (-item[1], item[0]))

    for i in sorted_resdict:
        print(i[0], end='')
    

if __name__ == "__main__":
    func()