Find Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one number that is missing from the array. Use the sum formula: sum(0 to n) = n*(n+1)/2 Example: [3,0,1] → Missing is 2 (expected: 0,1,2,3)

Input

Line 1: n. Line 2: n space-separated integers.

Output

The missing number.

Sample

3
3 0 1

Expected

2