GameObject FindClosestEnemy()
{
    GameObject[] gos;
    gos = GameObject.FindGameObjectsWithTag("Enemy");
    GameObject closest = null;
    float distance = Mathf.Infinity;
    Vector3 position = transform.position;
    foreach (GameObject go in gos)
    {
        Vector3 diff = go.transform.position - position;
        float curDistance = diff.sqrMagnitude;
        if (curDistance < distance)
        {
            closest = go;
            distance = curDistance;
        }
    }
    return closest;
}