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())

# Calculate the number of 2x1 dominoes that can fit in a row of the board
# If the row has an odd number of squares, we can fit (n-1)/2 dominoes
# If the row has an even number of squares, we can fit n/2 dominoes
num_in_row = n // 2

# Calculate the total number of dominoes that can fit on the board
# If the board has an odd number of rows, we can fit (m-1)*num_in_row + (n//2) dominoes
# If the board has an even number of rows, we can fit m*num_in_row dominoes
total_num = m * num_in_row + (n % 2) * (m // 2)

print(total_num)
