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A10018 | A Problem about Polyline

时间限制1s
内存限制256MB
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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 $x$ .

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
C++ 编辑器
输入
输出