import cs1.Keyboard;
public class Pi4 {
   public static void main(String[] args) {
      System.out.println("This program estimates PI using an infinite series.");
      System.out.println("Enter number of terms, e.g. 1000");
      double nterms = Keyboard.readInt();
      int term = 1; double sum = 0.0; double tn;
      for (term=1; term<nterms; term++) {
         tn = 4.0/(2.0 * term - 1.0);
         if (term % 2 == 0) tn = -tn; // even terms are negative
         sum += tn;
//         System.out.println("term=" + term + "\t" + "value=" + tn + "\t" + "PI=" + sum);
      } 
      System.out.println("PI=" + sum);
   }
}