/* File: FibIt.java - March 2011 */
package l04;

/**
 * Compute and display the Fibonacci number of the input argument
 * using an iterative algorithm. Long values are returned so that
 * quite large inputs (e.g. 100) are possible.
 *
 * Sample usage: java l04.FibIt 5
 *
 * @author Michael Albert
 *
 */

public class FibIt{

   public static void main(String[] args) {

      int n = Integer.parseInt(args[0]);
      System.out.println("Fib(" + n + ") = " + fib(n));

   }

   public static long fib(int n) {

      // a and b will track a successive pair of Fibonacci numbers
      // The bounds on the for loop mean that at the end, b will be
      // the one we want
      long a = 1, b = 1;
      for(int i = 1; i < n; i++) {
         // We want the current b to become the new a
         // and the sum of current a and current b to be the new b
         long c = b;
         b += a;
         a = c;
      }

      return b;
   }

}