The missing number

Problem

A form has numbered pages from 0 to n. One page is missing from the stack of n pages. Print the missing page number.

Example

Input

3
3 0 1

Output

Page 2 is missing.

Try the problem first. Open one hint at a time.

Hint 1

The sum of 0 to n is known, but XOR also works and cannot get large.

Hint 2

XOR n, every index and every value together.

Write your Python code, run it on the examples and submit it to hidden tests.