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: Accepted)

#include <stdio.h>

int main(void){
  int a[3];
  int temp;
  for(int i = 0; i < 3; i++) scanf("%d", &a[i]);
  for(int i = 0; i < 3; i++){
    for(int j = i + 1; j < 3; j++){
      if(a[i] < a[j]){
	temp = a[i];
	a[i] = a[j];
	a[j] = temp;
      }
    }
  }
  int s = a[1] * a[2] / 2;
  printf("%d\n", s);
  return 0;
}