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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

public class Main {
	static long S;
	public static void main(String[] args) {
		final Scanner sc = new Scanner(System.in);
		long h = sc.nextInt();
		long w = sc.nextInt();
		long s1,s2,s3;
		long ans = Long.MAX_VALUE;
		S = h*w;
		for(int i = 1; i < h; i++) {//一つの長方形のhについて全探索
			s1 = w*i;
			s2 = w*((h-i)/2);
			ans = Math.min(ans, hikaku(s1,s2));
			s2 = (h-i)*(w/2);
			ans = Math.min(ans, hikaku(s1,s2));
		}
		for(int i = 1; i < w; i++) {
			s1 = h*i;
			s2 = h*((w-i)/2);
			ans = Math.min(ans, hikaku(s1,s2));
			s2 = (w-i)*(h/2);
			ans = Math.min(ans, hikaku(s1,s2));
		}
		System.out.println(ans);
	}
	static long hikaku(long a, long b) {
		long c = S-a-b;
		if(c<=0||a<=0||b<=0) return Long.MAX_VALUE;
		return Math.abs(Math.max(a, Math.max(b, c))-Math.min(a, Math.min(b, c)));
	}
}