IEnumerator Start() {
    yield return new WaitForEndOfFrame();
    Debug.Log("Once After Update");
}

void OnceAfterUpdate() {
    Debug.Log("OnceAfterUpdate");
}

void LateUpdate() {
    if (Time.frameCount == 1) OnceAfterUpdate();
}

    void ClampCamera() {

  var terrain = Terrain.activeTerrain;
  var size = terrain.terrainData.size;
  var pos = terrain.GetPosition();

  var x = Mathf.Clamp(transform.position.x, pos.x, pos.x + size.x);
  var z = Mathf.Clamp(transform.position.z, pos.z, pos.z + size.z);

  transform.position = new Vector3(x, transform.position.y, z);

    }