Problem:
Score : 100 points

Problem Statement

There is a right triangle ABC with ∠ABC=90°.

Given the lengths of the three sides, |AB|,|BC| and |CA|, find the area of the right triangle ABC.

It is guaranteed that the area of the triangle ABC is an integer.

Constraints

1 \leq |AB|,|BC|,|CA| \leq 100

All values in input are integers.

The area of the triangle ABC is an integer.

Input

Input is given from Standard Input in the following format:

|AB| |BC| |CA|

Output

Print the area of the triangle ABC.

Sample Input 1

3 4 5

Sample Output 1

6

This triangle has an area of 6.

Sample Input 2

5 12 13

Sample Output 2

30

This triangle has an area of 30.

Sample Input 3

45 28 53

Sample Output 3

630

This triangle has an area of 630.

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>

main()
{
	int array[256] ;
	int numcount ;
	int chcount ;

	scanf ( "%d", &array[0] ) ;

	numcount = 0 ;
	while ( 1 )
	{
		if ( array [ numcount ] % 2 )
		{
			array [ numcount + 1 ] = array [ numcount ] * 3 + 1 ;
		}
		else
		{
			array [ numcount + 1 ] = array [ numcount ] / 2 ;
		}
		numcount++ ;

		chcount = 0 ;
		while ( chcount < numcount )
		{
			if ( array [ chcount ] == array [ numcount ] )
			{
				printf ( "%d\n", numcount + 1 ) ;
				//chcount = 0 ;
				//while ( chcount <= numcount )
				//{
					//printf ( "array [ %d ] = %d\n", chcount, array [ chcount ] ) ;
					//chcount++ ;
				//}
				return 0 ;
			}
			chcount++ ;
		}
	}

}