Calculating Pi

this was an assignment i had todo today posting it here for no reason.
pretty much the program uses this weird algorithm.
http://mathworld.wolfram.com/GregorySeries.html
simply does pi = 4 * (1 - (1/3) + (1/5) - (1/7).......) etc
the more times you go through this pattern the more exact you get.

Code:

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import java.util.Scanner;

public class PiCalc {
   
    public static void main(String[] args) {
            Scanner keyb = new Scanner(System.in);
            double pi =0;
            double numer = 1;
            double denom = 1;
            System.out.println("Enter the Number of iterations: ");
            double counter = keyb.nextDouble();
            while(counter>0)
            {
                    pi+= numer/denom;
                    numer*=-1;
                    denom+=2;
                    counter--;
            }
            pi*=4.0;
            System.out.println("Pi Was Calculated As: " + pi);
    }
}

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ran program with these parameters

Enter the Number of iterations:
799999999
Pi Was Calculated As: 3.1415926548383024

i googled pi and found it to be
3.141592653589793238462643383279502884197169399375 10582097494459230781640628620899862803482534211706 79.....