// Exercise 3.9
public class ComputPI { //saved as "ComputPI.java"	
	public static void main (String[] args) {		
		int numTerms = 50000;		
		double sum = 0.0;		
		double PI;   
		//calculate PI		
		for (int denominator = 1; denominator <= numTerms; denominator++){
			if ( denominator % 4 == 1 ){                
				sum = sum + 1.0/denominator;            
			}else if( denominator % 4 == 3){
				sum = sum - 1.0/denominator;
			}					
		}		
		PI = sum * 4;		
		System.out.println("the value of PI is " + PI);	
	}
}