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B - Mex

Score : $200$ points

Problem Statement

You are given a sequence of length $N$ consisting of integers: $A=(A_1,\ldots,A_N)$.

Find the smallest non-negative integer not in $(A_1,\ldots,A_N)$.

Constraints

• $1 \leq N \leq 2000$
• $0 \leq A_i \leq 2000$
• All values in input are integers.

Input

Input is given from Standard Input in the following format:

$N$

$A_1$ $\ldots$ $A_N$

Output

Print the answer.

8
0 3 2 6 2 1 0 0

4

The non-negative integers are $0,1,2,3,4,\ldots$.
We have $0,1,2,3$ in $A$, but not $4$, so the answer is $4$.

3
2000 2000 2000

0