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(){
  int a[3];
  int i,tmp_max=0;
  int i_max;
  scanf("%d %d %d",&a[0],&a[1],&a[2]);
  for(i=0;i<3;i++){
    if(tmp_max<a[i]){
      tmp_max=a[i];
      i_max=i;
    }
  }
  if(i_max==0)printf("%d\n",a[1]*a[2]/2);
  else if(i_max==1)printf("%d\n",a[0]*a[2]/2);
  else if(i_max==2)printf("%d\n",a[1]*a[0]/2);
}