A. A Problem about Polylinetime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard outputThere is a polyline going through points (0, 0) – (x, x) – (2x, 0) – (3x, x) – (4x, 0) – ... - (2kx, 0) – (2kx + x, x) – .... We know that the polyline passes through the point (a, b). Find minimum positive value x such that it is true or determine that there is no such x.InputOnly one line containing two positive integers a and b (1 ≤ a, b ≤ 109).OutputOutput the only line containing the answer. Your answer will be considered correct if its relative or absolute error doesn't exceed 10 - 9. If there is no such x then output  - 1 as the answer.ExamplesInput3 1Output1.000000000000Input1 3Output-1Input4 1Output1.250000000000NoteYou can see following graphs for sample 1 and sample 3.     
Input3 1
Output1.000000000000
['geometry', 'math', '*1700']