rocket if fire 2 problems

ok im trying to make a rocket shoot out with this script when i click right click ( fire 2) but my version wont work it only happens when i left click. how do i instantiate this script when i click fire 2

var projectile : Rigidbody;
var initialSpeed = 20.0;
var reloadTime = 0.5;
var ammoCount = 20;
private var lastShot = -10.0;

function Fire () {
    // Did the time exceed the reload time?
    if (Time.time > reloadTime + lastShot && ammoCount > 0) {
        // create a new projectile, use the same position and rotation as the Launcher.
        var instantiatedProjectile : Rigidbody = Instantiate (projectile, transform.position, transform.rotation);

        // Give it an initial forward velocity. The direction is along the z-axis of the missile launcher's transform.
        instantiatedProjectile.velocity = transform.TransformDirection(Vector3 (0, 0, initialSpeed));

        // Ignore collisions between the missile and the character controller
        Physics.IgnoreCollision(instantiatedProjectile.collider, transform.root.collider);

        lastShot = Time.time;
        ammoCount--;
    }
}

Try:

function Update()
{
  if (Input.GetMouseButtonDown(1))
  {
    Fire();
  }
}

Check Edit -> project settings Input for what key you have for Fire1

And use this line: if (Input.GetButton ("Fire1")){ Shoot();}