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 nextInt();

int A, B;

int main(){
	A=nextInt();
	B=nextInt();
	printf("%d\n", A*B/2);
	return 0;
}

int nextInt(){
	int f=0; char c=getchar();
	while((c<'0')||('9'<c)){c=getchar();}
	while((c>='0')&&(c<='9')){f=f*10+(c-'0'); c=getchar();}
	return f;
}