Missing String

Given a string consisting of lowercase letters only, find the typographically smallest string not present as a substring in it.

Given two string S₁ and S₂. S₁ is considered typographically smaller than S₂ if either:

• |S₁|<|S₂|
• |S₁|=|S₂|
• S₁ is lexicographically smaller than S₂

Input:

The first line of input contains the string S.

Output:

Answer as stated above.

Constraints:

1|S|10⁵

SAMPLE INPUT

saurabh

SAMPLE OUTPUT

c

Explanation

The given string saurabh , does not contain c hence answer is c.