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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
using namespace std;

static const int MAX = 1000000;

int main() {
	int s, a[MAX];
	cin >> s;
	a[0] = s;
	
	if(s == 1 || s == 2){
		cout << "4" << endl;
		return 0;
	}
	
	for(int i = 1; i < MAX; i++)
	{
		if(a[i-1] % 2 == 0){
			a[i] = a[i-1] / 2;
		}else if(a[i-1] % 2 != 0){
			a[i] = (a[i-1] * 3) + 1;
		}
		//cout  << " " << a[i] << " ";
		if(a[0] == 4){
			cout << "4" << endl;
			break;
		}
		if(a[i] == 4){
			cout << i + 4 << endl;
			break;
		}
	}
	return 0;
}