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.
LETTERS = [chr(x) for x in range(97,123)]
LETTERS.reverse()
def strongest(text):
    sub = list(text)
    out = []
    con = 0
    while con < len(LETTERS):
        if LETTERS[con] in text:
            out.append(LETTERS[con])
            text = text[text.index(LETTERS[con]):]
        con +=1	
    return "".join(out)  


test = raw_input()    
text = raw_input()
print strongest(text)