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
