字符统计

while Ture:
    try:
        s = input()
        a = sorted(s,key=ord)
        dict = {}
        for i in a:
        if i.isalpha() or i.isspace() or i.isdigit():
            if i not in dict.keys():
                dict[i] = 1
            else:
                dict[i] += 1
        b =sorted(dict.items(),key=lambda x:x[1],reverse=True)
        res=""
        for i in b:
            res+=i[0]
        print(res)
    except:
        break