302967: CF578A. A Problem about Polyline
Memory Limit:256 MB
Time Limit:1 S
Judge Style:Text Compare
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Description
A Problem about Polyline
题意翻译
现在有一条折线,它经过了点:(0,0)–(x,x)–(2x,0)–(3x,x)–(4x,0)–...-(2kx,0)–(2kx+x,x)–... 现在知道了这个折线经过点(a,b),找到最小的满足题意的x。如果没有这样的x输出-1。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 $ .输入输出格式
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
输入样例 #1
3 1
输出样例 #1
1.000000000000
输入样例 #2
1 3
输出样例 #2
-1
输入样例 #3
4 1
输出样例 #3
1.250000000000