The Missing Number

Difficulty: 1000 2000 ms 128 MB

math

The list should contain every integer from 1 to N exactly once, but one number is missing (so N−1 numbers are given). Find it.

Input: the first line has N; the second line has the N−1 remaining integers (empty when N = 1).

Output: the missing integer.

Constraints:

• 1 ≤ N ≤ 2000

Sample Tests

5
2 3 1 5

4

2
2

1

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