public class Fibo {

  public static void main(String[] args) {
    long n = 0;
    try {
      n = Long.parseLong(args[0]);
    } catch (Exception e) {
      System.out.println("input error: not an integer");
      return;
    }

    if (n < 0) {
      System.out.println("input error: negative input value");
    } else {
      System.out.format("fiboIt(%d)=%d\n", n, fiboIt(n));
    }
  }

  /*
   * Computes the n-th fibonacci number iteratively
   */
  public static long fiboIt(long n) {
    long currentNMinusOne = 1;
    long currentNMinusTwo = 0;
    long currentN = 1;
    for (int i = 0; i < n ; i++) {
      currentN = currentNMinusOne + currentNMinusTwo;
      currentNMinusOne = currentN;
      currentNMinusTwo = currentNMinusOne;
    }
    return currentN;
  }

}