public class DoublingExperiment { 
      static long fib(int n) {
        if (n < 2)
            return n;
        long prev = 0;
        long curr = 1;
        for (int i = 2; i <= n; i++) {
            curr = curr + prev;
            prev = curr - prev;
        }
        return curr;
    }

    public static void main(String[] args) { 
        long value;
        double time;
        int start = 2 << 20;
        int stop = 2 << 28;
        for (int n = start; n <= stop; n <<= 1) {
            Stopwatch sw1 = new Stopwatch();
            value = fib(n);
            time = sw1.elapsedTime();
            System.out.printf("n = %d, running time = %.2f%n", n, time);
        }
    }
}