Single Number

Problem Description

Given an array of integers A, every element appears twice except for one. Find that integer that occurs once.

NOTE: Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Problem Constraints

1 <= |A| <= 2000000
0 <= A[i] <= INTMAX

Input Format

The first and only argument of input contains an integer array A.

Output Format

Return a single integer denoting the single element.

Example Input

Input 1:
A = [1, 2, 2, 3, 1]

Input 2:
A = [1, 2, 2]

Example Output

Output 1:
3

Output 2:
1

Example Explanation

Explanation 1:
3 occurs once.

Explanation 2:
1 occurs once.

Output