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 Python (3.8.2) (judge verdict: Runtime Error)

n = int(input())
Hs = list(map(int,input().split()))
f = [0 for _ in range(n)]
r = 1
c = 0
while r != n:
    r = 1
    for i in range(n):
        if f[i] < Hs[i] :
            if r > 0:
                c += 1
            r = 0
            f[i] += 1
        else:
            r += 1
    r -= 1   
print(c)