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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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Sample cases (from the problem)
Sample Case 1
Input
12345
Expected output
3
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