import sys
while True:
try:
s = input()
dic = {}
for c in s:
dic[c] = s.count(c)
#按次数排序
ss = sorted(s, key = lambda x: dic[x])
min_count = dic[ss[0]]
#把等于最小次数的字符删掉
for c in ss:
if dic[c] == min_count:
s = s.replace(c, '')
else:
break
print(s)
except:
# print(sys.exc_info())
break



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