A^B == B^A?

Solve the equation in the name of this problem.

Input

There are several cases. Each of them has a single real number as the smaller one of a and b in the equation on a separate line. You may assume it's no smaller than 1.1. Proceed until the end of file.

Output

For each case, print the other number on a single line. Keep 5 digits after decimal point. If no such number exists, print -1.

Sample Input

2
10
Sample Output

4.00000
-1

http://www.cnitblog.com/Acrux/archive/2008/02/11/39676.html