Problem Description

Hanako is looking at a sequence of numbers.

She performs the following operations on the sequence:

1. Select several elements that are not adjacent to each other.
2. Arrange the selected numbers in the order they appear in the sequence.
3. Read the arranged numbers as a decimal number.

Hanako is curious about what the smallest positive integer is that she cannot create with these operations.

For example, given the sequence "3 0 1", the positive integers Hanako can create are $1$, $3$, $31$.

In this case:

• $1$ can be created, but $2$ cannot be created because it does not appear in the sequence.
• Positive integers like "$13$" that ignore the order of appearance in the sequence cannot be created.
• Numbers like "$30$" or "$301$" that use adjacent digits cannot be created.

Please help Hanako find the smallest positive integer that cannot be created.

Input Format

$ n $ $ d_1 $ $ d_2 $ $ d_3 $ ... $ d_n $

• The first line contains the length of the sequence $n\ (1\ \leq\ n\ \leq\ 10000)$.
• The second line contains the sequence ($ d_1 $ $ d_2 $ ... $ d_n $) separated by spaces. $d_i\ (i\ =\ 1\ ,\ ...\ ,\ n\ )$ are digits between $0$ and $9$.

Output Format

Output the smallest positive integer that Hanako cannot create. Be careful not to output extra leading zeros. End the output with a newline.

Sample Input and Output

Sample Input #1

3
3 0 1

Sample Output #1

2

Sample Input #2

12
1 2 1 2 3 4 5 6 7 8 9 0

Sample Output #2

21

Sample Input #3

20
1 2 3 4 5 6 7 8 9 1 1 2 3 4 5 6 7 8 9 0

Sample Output #3

100

Notes/Hints

None

见题面 Input 部分

见题面 Output 部分