x = input()
if len(x) in range(1,21) and x.islower():
strs = list(x)
word = list(set(strs))
counta = {} # 创建一个字典, 记录每个字母出现的次数
for i in word:
counta[i] = x.count(i)
minwords = min(counta.values()) # 找出最少出现次数
for k,v in counta.items():
if v == minwords: # 找出最少出现次数的字母
for times in range(v): ### 根据元素的个数, 删除k(目标字母)多少次
strs.remove(k)
print("".join(strs))



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