Camera movement not restricting with clamp

I am building a load runner type game. The Camera is made a child object under the player. The player can move till -19.5 and 16 on x axis and 3 and 17.9 on y axis. The camera should follow (center) the player but should stop centering the player or move beyond the given x values or end of the scene built. But the camera is moving beyond the scene to show empty spaces. The camera is clamped in the player script as follows

void Start()

{

cam = GameObject.FindGameObjectWithTag("Player").transform.GetChild(0).gameObject;

     Vector3 v3 = cam.transform.position;

     v3.x = Mathf.Clamp(v3.x, -19.5f, 16f);

     v3.y = Mathf.Clamp(v3.y, 3f, 17.9f);

     cam.transform.position = v3;

rest of the code ,.... }