from math import ceil

def main():
    x, y = [int(i) for i in input().split()]

    if x==y:
        return x

    c = ceil(x / (2*y))
    if x < y:
        return -1

    if c > (x+y)/(2*x):
        print(c, (x+y)/(2*x))
        c = ceil((x+y)/(2*x))

    return (x+y)/(2*c)


print(main())