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Problem

Read a natural number n and compute its alternating digit sum,

starting from the most significant digit (leftmost) with a + sign;

signs then alternate: +, -, +, -, ...

For the number 12345, the alternating sum is 1 - 2 + 3 - 4 + 5 = 3.

Input format

Input input.txt

The program reads from standard input a single natural number `n`. - `0 <= n <= 1000000000` - if `n = 0`, the sum is `0`

Output format

Output output.txt

The program prints a single integer: the alternating digit sum, followed by a newline.

Example

input
12345
output
3

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📚 Call Stack
main() line 1
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