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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

	import java.math.BigDecimal;
	import java.util.ArrayList;
	import java.util.Collections;
	import java.util.Comparator;
	import java.util.HashMap;
	import java.util.List;
	import java.util.Scanner;
	import java.util.regex.Matcher;
	import java.util.regex.Pattern;
	
	
	public class Main {
		static Scanner sc = new Scanner(System.in);
	
		public static void main (String [] args){
			//		String [][] boad = new String[4][4];
			int n = Integer.parseInt(sc.next());
			int m = Integer.parseInt(sc.next());
			List <Integer> list = new ArrayList<Integer>();
			int total = 0;
			int c = 0;
			total = (n*m)/2;
			
			System.out.println(total);
			System.out.flush();
			sc.close();
		}
	}