Woburn Challenge 2018-19 Round 4 - Junior Division

Billy, the king of video games, began his career off the back of a particular arcade game: Donkey Kong. Though he's masterfully played many other games since, there's nothing quite like popping in a few quarters and returning to the arcade classic.
Beginning a game of Donkey Kong requires the player to first insert at
least
What's the minimum number of additional quarters which Billy must insert
such that the total amount of inserted change will come out to at least
Input Specification
The first line of input consists of a single integer,
The next line consists of a single integer,
Output Specification
Output a single integer, the number of additional quarters which Billy must insert.
Sample Input 1
2
3
Sample Output 1
5
Sample Input 2
1
20
Sample Output 2
0
Sample Explanation
In the first case, Billy has already inserted
In the second case, Billy has already inserted at least
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