def GrowInstanceDisk(r, instance, disk, amount, wait_for_sync=False):
    """
    Grows a disk of an instance.

    More details for parameters can be found in the RAPI documentation.

    @type instance: string
    @param instance: Instance name
    @type disk: integer
    @param disk: Disk index
    @type amount: integer
    @param amount: Grow disk by this amount (MiB)
    @type wait_for_sync: bool
    @param wait_for_sync: Wait for disk to synchronize
    @rtype: int
    @return: job id
    """
    body = {'amount': amount, 'wait_for_sync': wait_for_sync}
    return r.request('post', '/2/instances/%s/disk/%s/grow' % (instance,
        disk), content=body)
