'''
a='aabcddd'
b=a.replace('b','')
print(b)
print(a.count('d'))
'''

string=str(input())
cnt={}
for i in string:
    cnt[i]=string.count(i)
cnt_min=min(cnt.values())
#print(cnt_min)
for key in cnt.keys():
    if cnt[key]==cnt_min:
        string=string.replace(key,'')
print(string)