You are given a rectangular board of *M* × *N* squares. Also you are given an unlimited number of standard domino pieces of 2 × 1 squares. You are allowed to rotate the pieces. You are asked to place as many dominoes as possible on the board so as to meet the following conditions:

1. Each domino completely covers two squares.

2. No two dominoes overlap.

3. Each domino lies entirely inside the board. It is allowed to touch the edges of the board.

Find the maximum number of dominoes, which can be placed under these restrictions.
In a single line you are given two integers *M* and *N* — board sizes in squares (1 ≤ *M* ≤ *N* ≤ 16).
m, n = map(int, input().split())

# Each horizontal domino covers 2 squares
# Each vertical domino covers 1 square
# So, to cover the board optimally, we should first try to place as many
# horizontal dominoes as possible, and then place the remaining vertical
# dominoes to cover the remaining squares.

# Count the number of horizontal and vertical squares
num_horiz_squares = (n // 2) * m
num_vert_squares = (m // 2) * (n % 2)

# Add the remaining horizontal squares, if any
if n % 2 == 1:
    num_horiz_squares += (m // 2)

# The total number of squares covered by dominoes is the sum of horizontal
# and vertical squares
num_covered_squares = num_horiz_squares + num_vert_squares

print(num_covered_squares)
