1144 The Missing Number （20 分）
Given N integers, you are supposed to find the smallest positive integer that is NOT in the given list.
Each input file contains one test case. For each case, the first line gives a positive integer N (≤105). Then N integers are given in the next line, separated by spaces. All the numbers are in the range of int.
Print in a line the smallest positive integer that is missing from the input list.