CF1152C Neko does Maths

Neko loves divisors. During the latest number theory lesson, he got an interesting exercise from his math teacher. Neko has two integers $ a $ and $ b $ . His goal is to find a non-negative integer $ k $ such that the least common multiple of $ a+k $ and $ b+k $ is the smallest possible. If there are multiple optimal integers $ k $ , he needs to choose the smallest one. Given his mathematical talent, Neko had no trouble getting Wrong Answer on this problem. Can you help him solve it?

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In the first test, one should choose $ k = 2 $ , as the least common multiple of $ 6 + 2 $ and $ 10 + 2 $ is $ 24 $ , which is the smallest least common multiple possible.