def pp(c)
    c.each do |l|
        puts l
    end
end
$dx = [0,1,0,-1]
$dy = [1,0,-1,0]
$m = Array.new
def fill(c,i,j,ch,h,w)
    q = [[i,j]]
    while q.size > 0
        sy, sx = q.shift
        c[sy][sx] = ch
        $m.push([sy,sx])
        for i in 0..3
            cy = sy + $dy[i]
            cx = sx + $dx[i]
            if cy.between?(0,h-1) && cx.between?(0,w-1) && c[cy][cx]=="."
                q.push([cy,cx])
            end
        end
    end
end

w, h = gets.split.map(&:to_i)
c = h.times.map{gets.chomp}
bl = false
c.each_with_index do |line,i|
    line.each_char.with_index do |cc,j|
        next unless cc == "."
        fill(c,i,j,"0",h,w)
        bl = true
        break
    end
    break if bl
end
#pp c
bl = false
ret = 0
while $m.size > 0
    sy, sx = $m.shift
    for i in 0..3
        cy = sy + $dy[i]
        cx = sx + $dx[i]
        if c[cy][cx] == "."
            ret = c[sy][sx].to_i
            bl = true
            break
        elsif cy.between?(1,h-2) && cx.between?(1,w-2) && c[cy][cx]=="\#"
            $m.push([cy,cx]) if !$m.include?([cy,cx])
            c[cy][cx] = (c[sy][sx].to_i + 1).to_s
        end
    end
    break if bl
end
p ret