Find the Missing Number in a Sequence

Given a single line of space-separated integers in ascending order, one number in the complete sequence is missing. Your task is to identify and output this missing number.

For example, if the input is "1 2 3 5 6", then the missing number is 4 because the natural consecutive order should be 1, 2, 3, 4, 5, 6.

Note: The input will always have at least two numbers and exactly one missing number in the sequence.

inputFormat

The input consists of a single line containing space-separated integers in ascending order. All integers are guaranteed to represent a nearly consecutive sequence with exactly one missing number between the smallest and largest element.

Example: 1 2 3 5 6

outputFormat

Output the missing integer in the sequence.

Example Output: 4

1 2 3 5 6

4