koosaga is drawing a logo for the next iteration of the KAIST contest. He has gotten lazy, so he has taken a rectangle of length ~X~ and height ~Y~ and drawn the two diagonals of the rectangle, forming four small triangles. He wishes to know the area of one of these triangles in the figure he has drawn.

Constraints

~1 \le X, Y \le 10^9~

In tests worth 14 marks, ~\max(X, Y) \le 10~.

Input Specification

The input will consist of two positive integers, ~X~ and ~Y~, ~X~ on the first line and ~Y~ on the second.

Output Specification

Output, on a single line, the area of one of the given triangles. The area must be printed with exactly two digits after the decimal point.

Sample Input

2
2

Sample Output

1.00