($w,$h)=<>=~/\d+/g;
$/=\1;
for$y(1..$h){
    for$x(1..$w+1){
	$f{$x,$y}=<>;
    }
}
l1:{
    for$y(1..$h){
	for$x(1..$w){
	    if($f{$x,$y}eq'.'){
		$f{$x,$y}=A;
		last l1;
	    }
	}
    }
}
for$y(1..$h){
    for$x(1..$w){
	if($f{$x,$y}eq'.'){
	    if($f{$x-1,$y}eq A || $f{$x+1,$y}eq A || $f{$x,$y-1}eq A || $f{$x,$y+1}eq A ){
		$f{$x,$y}=A;
	    }
	}
    }
}
for$l(0..99){
    for$y(1..$h){
	for$x(1..$w){
	    if($f{$x,$y}eq 'A'){
		if($f{$x-1,$y}eq '.'|| $f{$x+1,$y}eq '.' || $f{$x,$y-1}eq '.' || $f{$x,$y+1}eq '.' ){
		    print $l;
		    exit;
		}
		if($f{$x-1,$y}eq'#'){
		    $f{$x-1,$y}=B;
		}
		if($f{$x+1,$y}eq'#'){
		    $f{$x+1,$y}=B;
		}
		if($f{$x,$y-1}eq'#'){
		    $f{$x,$y-1}=B;
		}
		if($f{$x,$y+1}eq'#'){
		    $f{$x,$y+1}=B;
		}
	    }
	}
    }
    for$y(1..$h){
	for$x(1..$w){
	    if($f{$x,$y}eq B){
		$f{$x,$y}=A;
	    }
	}
    }
}