B'Tanya is learning how to add numbers, but so far she is not doing it correctly. She is adding two numbers a and b using the following algorithm: For example, the numbers a = 17236 and b = 3465 Tanya adds up as follows: large{ begin{array}{r} + begin{array}{r} 17236 03465 end{array} hline begin{array}{r} 1106911 end{array} end{array}} As a result, she gets 1106911 . You are given two positive integers a and s . Find the number b such that by adding a and b as described above, Tanya will get s . Or determine that no suitable b exists. The first line of input data contains an integer t ( 1 <= t <= 10^4 ) -- the number of test cases. Each test case consists of a single line containing two positive integers a and s ( 1 <= a lt s <= 10^{18} ) separated by a space. For each test case print the answer on a separate line. If the solution exists, print a single positive integer b . The answer must be written without leading zeros. If multiple answers exist, print any of them. If no suitable number b exists, output -1. The first test case is explained in the main part of the statement. In the third test case, we cannot choose b that satisfies the problem statement. '...