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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>

int main()
{
	int s;
	scanf("%d",&s);
	int a[1000000];
	a[0]=s;
	int judge=0;
	int ans;
	for (int i = 1; i < 1000000; ++i)
	{
		if(a[i-1]%2==0){
			a[i]=a[i-1]/2;
		}else{
			a[i]=a[i-1]*3+1;
		}
		for (int j = 0; j < i; ++j)
		{
			if(a[i]==a[j]){
				judge++;
			}
		}
		if(judge!=0){
			printf("%d",ans);
			break;
		}
	}
	return 0;
}