There is a polyline going through points (0, 0) – (*x*, *x*) – (2*x*, 0) – (3*x*, *x*) – (4*x*, 0) – ... - (2*kx*, 0) – (2*kx* + *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*.
Only one line containing two positive integers *a* and *b* (1 ≤ *a*, *b* ≤ 10<sup class="upper-index">9</sup>).
import sys
from math import sqrt

x, y = [int(x) for x in sys.stdin.readline().split()]

if y > x:
    print(-1)
    exit()

s = (x + y) / 2
r = (x - y) / 2

ans = min(s / int(s / y), r / int(r / y))
print(ans)
