Find the Duplicate Number

Problem statement

A locker scan produces n + 1 labels, each between 1 and n. Exactly one distinct label is repeated, possibly more than twice; all other labels appear at most once. Identify the repeated label without modifying the scan and using constant extra space.

Input format

First line: n. Second line: n + 1 integers.

Output format

Print the repeated label.

Constraints

1 <= n <= 100000; 1 <= label <= n; exactly one distinct repeated label.

Sample input

5
4 2 5 1 3 2

Sample output

2