[BOJ] 14502. 연구소

import java.util.Scanner;

public class Main {
	static int N, M;
	static int[][] map;
	static int[][] copy;	
	static int[] dy = {1, 0, -1, 0};
	static int[] dx = {0, 1, 0, -1};
	static int result = Integer.MIN_VALUE;
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		N = sc.nextInt();
		M = sc.nextInt();
		map = new int[N][M];
		copy = new int[N][M];
		for(int i = 0; i < N; i++) {
			for(int j = 0; j < M; j++) {
				map[i][j] = sc.nextInt();				
			}
		}
				
		wall(0);
		System.out.println(result);
	}
	
	static void wall(int depth) {
		if(depth == 3) {			
			copyMap();			
			
			for(int i = 0; i < N; i++) {
				for(int j = 0; j < M; j++) {
					if(copy[i][j] == 2) {
						dfs(i,j);						
					}
				}
			}
			result = Math.max(result, count());			
			return;
		}
		
		for(int i = 0; i < N; i++) {
			for(int j = 0; j < M; j++) {
				if(map[i][j] == 0) {
					map[i][j] = 1;
					wall(depth+1);
					map[i][j] = 0;
				}
			}
		}
	}
	
	static void dfs(int y, int x) {				
		for(int i = 0; i < dy.length; i++) {
			int ny = y + dy[i];
			int nx = x + dx[i];
			if(ny < 0 || ny >= N || nx < 0 || nx >= M) continue;
			if(copy[ny][nx] == 0) {
				copy[ny][nx] = 2;
				dfs(ny, nx);
			}
		}
	}
	
	static void copyMap() {
		for(int i = 0; i < N; i++) {
			for(int j = 0; j < M; j++) {
				copy[i][j] = map[i][j];
			}
		}
	}
	
	static int count() {
		int cnt = 0;
		for(int i = 0; i < N; i++) {
			for(int j = 0; j < M; j++) {
				if(copy[i][j] == 0) cnt++;
			}
		}
		return cnt;
	}
}