{"raw_statement":[{"iden":"problem statement","content":"Takahashi is playing billiards on a two-dimensional plane. The $x$\\-axis functions as a wall; when a ball hits the axis, it will bounce off the axis so that the angle of incidence equals the angle of reflection.\nTakahashi's ball is now at $(S_x,S_y)$. When he strikes the ball aiming for some point, it will roll in a straight line towards that point.\nTo make the ball hit the $x$\\-axis exactly once and then pass $(G_x, G_y)$, where along the $x$\\-axis should he aim for?"},{"iden":"constraints","content":"*   $-10^6 \\leq S_x, G_x \\leq 10^6$\n*   $0 < S_y, G_y \\leq 10^6$\n*   $S_x \\neq G_x$\n*   All values in input are integers."},{"iden":"input","content":"Input is given from Standard Input in the following format:\n\n$S_x$ $S_y$ $G_x$ $G_y$"},{"iden":"sample input 1","content":"1 1 7 2"},{"iden":"sample output 1","content":"3.0000000000\n\nAs shown below, we can make the ball pass $(7, 2)$ by striking it aiming for $(3, 0)$.\n![image](https://img.atcoder.jp/ghi/c9595d59f1139b808d4cf3d31d6b48ee.png)"},{"iden":"sample input 2","content":"1 1 3 2"},{"iden":"sample output 2","content":"1.6666666667\n\n![image](https://img.atcoder.jp/ghi/4f2c808fddc9bb349999f8969996ebb9.png)"},{"iden":"sample input 3","content":"\\-9 99 -999 9999"},{"iden":"sample output 3","content":"\\-18.7058823529\n\nThe output will be considered correct when its absolute or relative error from our answer is at most $10^{-6}$."}],"translated_statement":null,"sample_group":[],"show_order":["default"],"formal_statement":null,"simple_statement":null,"has_page_source":true}