import java.util.ArrayList;
 
public class Main
{
  /**
   * The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17
   * Find the sum of all the primes below two million.
   * @param args
   */
  public static void main(String[] args)
  {
    ArrayList<Integer> primes = new ArrayList<Integer>();
    int upper = 5000;
    for (int i = 2; i < upper; i++)
    {
      primes.add(i);
    }
    long sum = 0;
    for (int i = 0; i < primes.size(); i++)
    {
      if (true)   // (isPrime(primes.get(i)))
      {
        for (int k = 2; k*primes.get(i) < upper; k++)
        {
          if (primes.contains(k*primes.get(i)))
          {
            primes.remove(primes.indexOf(k*primes.get(i)));
          }
        }
      }
    }
    for (int i = 0; i < primes.size(); i++)
    {
      sum += primes.get(i);
    }
    System.out.println(sum);
  }
 
  public static boolean isPrime(int number)
  {
    for (int i = 2; i <= Math.sqrt(number); i ++)
    {
      if (number % i == 0)
      {
        return false;
      }
    }
    return true;
  }
}

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5k  0.26s-381MB   
10k 0.84s-380MB   N^1.70  .... 2mln:  1h 55'
20k 3.09s-380MB   N^1.88  .... 2mln:  4h 55'   projection worsening
40k 12.81-380     N^2.05  .... 2mln: 10h 50'   projection worsening still ...