import re
from collections import Counter


a=input()
b=re.findall('(.*?)',a)
#print(b)
c=[]
for t in b:
    if t !='' :
        c.append(t)
d=Counter(c)
f=min(d.values())
#print(f)
g=[]
kk=[]
for y in d.keys():
    if d[y]==f:
        g.append(y)
for p in c:
    if p not in g:
        kk.append(p)
mm=''
for u in kk:
    mm=mm+str(u)
print(mm)