Permutation

A sequence of $n$ positive integers is given. Determine whether it is a permutation of the first $n$ positive integers.

Input

The first line contains the integer $n(n\le 10000)$, followed by a sequence of $n$ positive integers. It is known that each of these numbers does not exceed $2\cdot 10^6$.

Output

Print $0$ if the sequence is a permutation. Otherwise, print the smallest number that is missing from the sequence.

Examples