Problem Statement

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.

Takahashi'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.

To 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?

Constraints

• $-10^6 \leq S_x, G_x \leq 10^6$
• $0 < S_y, G_y \leq 10^6$
• $S_x \neq G_x$
• All values in input are integers.

Input

Input is given from Standard Input in the following format:

S_x S_y G_x G_y

Output

Let $(x, 0)$ be the point Takahashi should aim for. Print $x$.

Your output will be considered correct when its absolute or relative error from our answer is at most $10^{-6}$.