Alice has a right angled triangle with integer side lengths. Given the lengths of the three sides of the triangle, find the area of the triangle.

Input Specification

The first line will contain ~3~ integers, ~a, b, c~ ~(1 \le a, b, c \le 2~ ~000)~, the three side lengths of the triangle.

It is guaranteed that the side lengths will form a valid right angle triangle.

Output Specification

Output the area of the triangle, rounded to the nearest integer.

Sample Input 1

12 13 5

Sample Output 1

30

Sample Input 2

25 24 7

Sample Output 2

84