A booth issues numbered ticket stubs 0, 1, 2, \dots, n (that is, n + 1 stubs in total). At closing time the clerk's log should contain all n + 1 stub numbers, but exactly one entry was never logged, so the log holds only n of the n + 1 values (all distinct, each in the range [0, n]).
Given the log, determine which single stub number is missing.
Input format
Line 1: an integer n.
Line 2: n space-separated distinct integers, each in [0, n] (this line is empty when n = 0).
Output format
A single integer: the one value in [0, n] that does not appear in the log.
Constraints
- 0 ≤ n ≤ 100000