Maga and Alex are good at string manipulation problems. Just now they have faced a problem related to string. But it is not a standard string problem. They have no idea to solve it. They need your help.

A string is called unique if all characters of string are distinct.

String s_1 is called subsequence of string s_2 if s_1 can be produced from s_2 by removing some characters of s_2.

String s_1 is stronger than s_2 if s_1 is lexicographically greater than s_2.

You are given a string. Your task is to find the strongest unique string which is subsequence of given string.

Input:

first line contains length of string.
second line contains the string.

Output:

Output the strongest unique string which is subsequence of given string.

Constraints:

1 ≤ |S| ≤ 100000   

All letters are lowercase English letters.

SAMPLE INPUT
5
abvzx

SAMPLE OUTPUT
zx

Explanation

Select all subsequence of the string and sort them in ascending order. The greatest of all is zx.
from sys import stdin
pr = ''
n = int(stdin.readline())
a = stdin.readline().strip()
s = set()
di = {}
for i in xrange(n):
	x = di.get(a[i],[])
	x.append(i)
	di[a[i]] = x
ans = ''
b = 'abcdefghijklmnopqrstuvwxyz'
b = list(b)
b.reverse()
b = ''.join(b)
ans = ''
pr = -1
#print di
for i in b:
	#print "checking ",i
	if di.get(i,0)==0:
		continue
	for u in di[i]:
	#	print i,di[i]
		if u > pr:
			pr = u
			ans += i
			#print " ans becomes ",ans
			break
print ans