test.php

<?php
//This code read the necessary data form the standard input

function isPrime($n) {
	if ($n == 1) return false;
	if($n == 2) return true;
  
	if ($n % 2 == 0) return false;
  
	for($i = 3; $i <= ceil(sqrt($n)); $i = $i + 2) {
		if($n % $i == 0) return false;
	}
  
  	return true; 
}

while ($line = trim(fgets(STDIN))) { 
    //$line contains the line of the input
  	//echo $line . "\n";
  
  	$current_num = 2; // Start find prime begin as 2
  	$sum = 0; // set default result
  	$counter = 0; // set counter = 0, its increament when a prime number has been sum
  	while ($counter <= intval($line)) {
   		if(isPrime($current_num)) $sum = $sum + $current_num;
  	}
  
  	echo $sum . "\n";
}