<>;
for(<>){
	($X,$Y)=split;
	$x=$X/20+1|0;
	$y=$Y/20+1|0;
	for$y($y-1..$y+1){
		for$x($x-1..$x+1){
			for(@{$_[$y][$x]}){
				if((@$_[0]-$X)**2+(@$_[1]-$Y)**2<400){
					goto a
				}
			}
		}
	}
	push@{$_[$y][$x]},[$X,$Y];
	++$z;
	a:
}
print$z