A20250417b_google_lexographicMax

'''
A20250417b_google_lexographicMax

find the lexographically max subsequence that can be formed from the string but the
twist each character in it should be unique

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important thing to be noted here is

first we need to understand the lexographic maximum

say abc

with this max string we can form is c

lets take cabcab

with this you can form cb

did you observe something there is some monotonocity in this

if you find monotonocity we can use kumar sir's stack approach

lets take a stack

traverse from left to right

for each character pop out while curr>=top (each char should be unique so that's why eliminating equals even)

at last put it on top




=======================================================
input -
abzdczzc

output -
zc

'''

arr = list(input())
stack = []
for charr in arr:
    # print('charr is ',charr)
    while len(stack)>0 and stack[-1]<=charr:
        curr = stack.pop()
        # print('curr is ',curr)
    stack.append(charr)

final = ''
while len(stack):
    curr = stack.pop()
    final = curr+final

print(final)