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:

\(\bullet |S_1| < |S_2| \\ \bullet |S_1| = |S_2| \text{ and } S_1 \text{is lexicographically smaller than } S_2\)

Input:

The first line of input contains the string S.

Output:

Answer as stated above.

Constraints:

\(1 \le |S| \le 10^5\)