<?php
	$r = 4;
	$tochnost = 1000000;
	function y($x) {
		global $r;
		return sqrt($r*$r-$x*$x);
	}
	for($i=-$r*$tochnost;$i<$r*$tochnost;$i++) {
		$x1 = $i/$tochnost;
		$y1 = y($x1);
		$x2 = ($i+1)/$tochnost;
		$y2 = y($x2);
		$d += sqrt(pow(($x2-$x1),2)+pow(($y2-$y1),2));
	}
	echo 'pi = '.$d/$r;
?>