JaeHyeonKim19

import java.io.*;
import java.util.Stack;
import java.util.StringTokenizer;

public class Main {
	public static void main(String[] args) throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		int m = Integer.parseInt(st.nextToken());
		int n = Integer.parseInt(st.nextToken());
		int [][] tomatoes = new int[n][m];
		for(int i = 0; i < n; i++) {
			st = new StringTokenizer(br.readLine());
			for(int j = 0; j < m;j++) {
				tomatoes[i][j] = Integer.parseInt(st.nextToken());
			}
		}
		Stack<int []> s = new Stack<int []>();
		int answer = 0;
		boolean flag = true;
		for(int i = 0; i < n;i++) {
			for(int j = 0; j < m;j++) {
				if(tomatoes[i][j] == 1) {
					if(i-1 >= 0 && tomatoes[i-1][j] == 0 ) {
						int [] coordinate = {i-1, j};
						s.push(coordinate);
					}
					if(j-1 >= 0 && tomatoes[i][j-1] == 0) {
						int [] coordinate = {i, j-1};
						s.push(coordinate);
					}
					if(i+1 < n && tomatoes[i+1][j] == 0) {
						int [] coordinate = {i+1, j};
						s.push(coordinate);
					}
					if(j+1 < m && tomatoes[i][j+1] == 0) {
						int [] coordinate = {i, j+1};
						s.push(coordinate);
					}
				} else if(tomatoes[i][j] == 0) {
					flag = false;
				}
			}
		}
		if(s.isEmpty()) {
			if(flag) {
				System.out.println(answer);
				return;
			} else {
				System.out.print(--answer);
				return;
			}
		}else {
			answer++;
		}
		Stack<int []> newS = new Stack<int []>();
		while(!s.isEmpty()) {
			int [] curCoordinate = s.pop();
			int i = curCoordinate[0];
			int j = curCoordinate[1];
			tomatoes[i][j] = 1;
			if(i-1 >= 0 && tomatoes[i-1][j] == 0 ) {
				tomatoes[i-1][j] = 1;
				int [] coordinate = {i-1, j};
				newS.push(coordinate);
			}
			if(j-1 >= 0 && tomatoes[i][j-1] == 0) {
				tomatoes[i][j-1] = 1;
				int [] coordinate = {i, j-1};
				newS.push(coordinate);
			}
			if(i+1 < n && tomatoes[i+1][j] == 0) {
				tomatoes[i+1][j] = 1;
				int [] coordinate = {i+1, j};
				newS.push(coordinate);
			}
			if(j+1 < m && tomatoes[i][j+1] == 0) {
				tomatoes[i][j+1] = 1;
				int [] coordinate = {i, j+1};
				newS.push(coordinate);
			}
			if(s.isEmpty() && !newS.isEmpty()) {
				answer++;
				while(!newS.isEmpty()) {
					s.push(newS.pop());
				}
			} else if(s.isEmpty() && newS.isEmpty()) {
				for(int x = 0; x < n; x++) {
					for(int y = 0; y < m; y++) {
						if(tomatoes[x][y] == 0) {
							System.out.print(-1);
							return;
						}
					}
				}
				System.out.print(answer);
			}
		}
	}
}