public class Prog5_25
{
	public static void main(String[] args)
	{
		System.out.println("This program will compute the value of pi through an estimation of the form 4 * (1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ...");
		int factor = 1;					// we will multiply factor by -1 so that it alternates adding and subtraction 1 / i to our value
		double pi = 0.0;
		for(int i=1;i<1000;i+=2)			// iterate by 2's
		{
			pi += factor * 1.0 / i;		// add next fraction 1 / i to pi, alternating + or - using factor
			factor *= -1;				// change factor from plus to minus or minus to plus
		}
		pi *= 4;						// finish off computation by multiplying by 4
		System.out.println("Estimate for pi is       " + pi);
		System.out.println("Actual value for pi is   " + Math.PI);
	}
}