#一开始以为要分三种情况，即abb,aabbddd,ddddd,后来发现不用,都用最后那几行统一处理即可
while True:
    try:
        s=input()
        ss=set(s)
        adict={}
        snew=''
        for i in ss:
            adict[i]=s.count(i)
        alist=sorted(adict.items(),key=lambda stu:stu[1])
        # print(alist)
        # if alist[0][1]<alist[1][1]:
        #     print(s.replace(alist[0][0],''))
        # elif alist[0]==alist[-1]:
        #     print()
        # else :
        subs = ''
        for item in alist:
            if item[1]==alist[0][1]:
                subs+=item[0]
        for i in subs:
            s=s.replace(i,'')
        print(s)
    except:
        break