Once an ACM programmer was driving along a highway. The road was very smooth and straight, no pits, no bumps, no turns miles and miles forward. In short, boring! So the programmer decided to view billboards along the highway. One billboard was so interesting that the programmer wanted to examine it properly. But without a computer he found it difficult to determine the point with the maximal viewing angle. \InputFile We regard the billboard as a segment on a plane and assume that the road is represented by the abscissa axis. The input consists of four lines with numbers \textbf{x_1}, \textbf{y_1}, \textbf{x_2}, \textbf{y_2}, which are the coordinates of the billboard's edges. The numbers are integers in the range from \textbf{−1000} to \textbf{1000}. Billboard's edges are not coincide. \OutputFile You should output the value (in radians) of the best viewing angle of the billboard from the road within \textbf{6} digits after the decimal point.