How to limit jumheight

I use this code for movement and jumping, I want it to jump not very high

public class movement : MonoBehaviour {
private Rigidbody rg;
public float speed = 10.0F;
public float jumpspeed = 10.0F;

void Start () {
    Cursor.lockState = CursorLockMode.Locked;
    rg = GetComponent <Rigidbody> ();
}


void Update () {
    float translation = Input.GetAxis ("Vertical") * speed;
    float straffe = Input.GetAxis ("Horizontal") * speed;
    translation *= Time.deltaTime;
    straffe *= Time.deltaTime;
   
    transform.Translate (straffe, 0, translation);
   
    if (Input.GetKey (KeyCode.Space)) {
        Vector3 atas = new Vector3 (0,100,0);
        rg.AddForce(atas * speed);
    }
   
    if (Input.GetKeyDown ("escape"))
        Cursor.lockState = CursorLockMode.None;
   
   
}

}

Have bool Jumped = false and when you press set it to true. When you land back on ground have colider to check did you land. When landed set isJumped back to =false.