Problem:
Score : 400 points

Problem Statement

There is a bar of chocolate with a height of H blocks and a width of W blocks.
Snuke is dividing this bar into exactly three pieces.
He can only cut the bar along borders of blocks, and the shape of each piece must be a rectangle.

Snuke is trying to divide the bar as evenly as possible.
More specifically, he is trying to minimize S_{max} - S_{min}, where S_{max} is the area (the number of blocks contained) of the largest piece, and S_{min} is the area of the smallest piece.
Find the minimum possible value of S_{max} - S_{min}.

Constraints

2 ≤ H, W ≤ 10^5

Input

Input is given from Standard Input in the following format:

H W

Output

Print the minimum possible value of S_{max} - S_{min}.

Sample Input 1

3 5

Sample Output 1

0

In the division below, S_{max} - S_{min} = 5 - 5 = 0.

Sample Input 2

4 5

Sample Output 2

2

In the division below, S_{max} - S_{min} = 8 - 6 = 2.

Sample Input 3

5 5

Sample Output 3

4

In the division below, S_{max} - S_{min} = 10 - 6 = 4.

Sample Input 4

100000 2

Sample Output 4

1

Sample Input 5

100000 100000

Sample Output 5

50000

Solution in Ruby (2.3.3) (judge verdict: Accepted)

h, w = gets.chomp.split(" ").map(&:to_i)

if h % 3 == 0 || w % 3 == 0
    puts 0
    exit
end

# 横に3等分
ans = w

# 縦に3等分
ans = h if h < ans

# 横に1/3してから残りを縦に2等分
h = h.to_f
w = w.to_f


s = [(h/3).ceil * w, (h-(h/3).ceil)*((w/2).ceil), (h-(h/3).ceil)*((w/2).floor)]
ans = s.max - s.min if s.max - s.min < ans

s = [(h/3).floor * w, (h-(h/3).floor)*(w/2).ceil, (h-(h/3).floor)*(w/2).floor]
ans = s.max - s.min if s.max - s.min < ans

# 縦に1/3してから残りを横に2等分
s = [(w/3).ceil * h, (w-(w/3).ceil)*(h/2).ceil, (w-(w/3).ceil)*(h/2).floor]
ans = s.max - s.min if s.max - s.min < ans

s = [(w/3).floor * h, (w-(w/3).floor)*(h/2).ceil, (w-(w/3).floor)*(h/2).floor]
ans = s.max - s.min if s.max - s.min < ans

puts ans.to_i