// Algorithm:
//
//	read input
//	First mark all warm squares (called external)
//	Loop while there is butter left
//	   mark all melting squares
//	   remove all melted butter (check if a hole is uncovered)
//	   increment num hours
//
//	print num hours


public class Butter
{
	static int R, C;

	// recursive method to check if adjacent squares are touching
	// an external square (Standard floodfill algorithm)
	static void checkExternal(Square [][] board, int i, int j)
	{
		if(!board[i][j].border
		   && !board[i][j].occupied
		   && !board[i][j].external)
		{
			board[i][j].external = true;
			// check all adjacent squares
			checkExternal(board, i+1, j);
			checkExternal(board, i-1, j);
			checkExternal(board, i, j+1);
			checkExternal(board, i, j-1);
		}
	}

	static void findExposed(Square [][] board)
	{
		// For each square, if occupied, check
		// if 2 adjacent are external
		for(int i = 2; i < R; i++)
			for(int j = 2; j < C; j++)
			{
				if(board[i][j].occupied)
				{
					int total = 0;
					if(board[i+1][j].external) total++;
					if(board[i-1][j].external) total++;
					if(board[i][j+1].external) total++;
					if(board[i][j-1].external) total++;
					if(total >= 2)
						board[i][j].exposed = true;
				}
			}
	}

	static void melt(Square [][] board)
	{
		// For each square, if exposed, check
		// if 2 adjacent are external
		for(int i = 2; i < R; i++)
			for(int j = 2; j < C; j++)
				if(board[i][j].exposed)
				{
					// remove from board.
					board[i][j].occupied = false;
					// Mark as external, (including any holes)
					checkExternal(board, i, j);
				}
	}

	// Debugging method
	static void print(Square [][] board)
	{
		for(int i = 1; i <= R; i++)
		{
			int j;
			for(j = 1; j < C; j++)
				if(board[i][j].occupied)
					System.out.print("1 ");
				else
					System.out.print("0 ");

			if(board[i][j].occupied)
				System.out.print("1");
			else
				System.out.print("0");
			System.out.println();			
		}

		System.out.println();			
	}

	static int count(Square [][] board)
	{
		int numOccupied = 0;
		for(int i = 1; i <= R; i++)
			for(int j = 1; j <= C; j++)
				if(board[i][j].occupied)
					numOccupied++;

		return numOccupied;
	}

	public static void main(String [] args)
	{
		R = Console.readInt();
		C = Console.readInt();

		// Initialise the board
		Square [][] board = new Square[R + 2][C + 2];
		for(int i = 0; i < R + 2; i++)
			for(int j = 0; j < C + 2; j++)
				board[i][j] = new Square();

		for(int i = 1; i <= R; i++)
			for(int j = 1; j <= C; j++)
				board[i][j].border = false;

		// Now mark in all the squares
		for(int i = 1; i <= R; i++)
			for(int j = 1; j <= C; j++)
				if(Console.readInt() == 1)
					board[i][j].occupied = true;

		// Mark all external squares
		checkExternal(board, 1, 1);
		
		int hours = 0;
		// Keep going as long as there is some butter left
		while(count(board) > 0)
		{
			hours++; // another hour passed.
			// Now find any exposed squares
			findExposed(board);
			// Melt the exposed squares
			melt(board);
		}

		System.out.println(hours);
	}
}

class Square
{
	boolean external;
	boolean border;
	boolean occupied;
	boolean exposed;

	Square() { external = false; border = true; occupied = false; exposed = false;}
}