s = input()

# 将输入的字符串转换成字典
sd = {}

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

# print(sd)   # {'a': 2, 'd': 3, 'c': 3}

# 根据value值对字典排序,如果value值相同,则根据keys升序排序
# item[1]降序,item[0]升序
sd_new = dict(sorted(sd.items(),key=lambda item:(-item[1],item[0])))

for key in sd_new.keys():
    print(key,end='')