A10018. A Problem about Polyline
编程题
普及/提高-
知识点
题目描述
There 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 $x$ .
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 $x$ .
输入格式
Only one line containing two positive integers $a$ and $b$ ( $1<=a,b<=10^{9}$ ).
输出格式
Output 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.
输入输出样例
输入 #1
3 1
输出 #1
1.000000000000
输入 #2
1 3
输出 #2
-1
输入 #3
4 1
输出 #3
1.250000000000
说明/提示
You can see following graphs for sample 1 and sample 3.
 
 