Serial Number Alternating Checksum

Each item leaving a warehouse is stamped with a positive integer serial number. To help catch scanning errors, the warehouse computes an alternating checksum from the serial number's digits: reading the digits from left (most significant) to right, the first digit is added, the second digit is subtracted, the third digit is added, and so on, with the sign alternating for every subsequent digit.

Given a serial number, compute its alternating checksum.

Input format

A single line containing one integer n, the serial number.

Output format

Print a single integer: the alternating checksum of n's digits. The result may be negative.

Constraints

• 1 <= n <= 10^9

886996

0

15

-4