how to stop double jumping in unity code example

Example: remove double jump unity

using UnityEngine; using System.Collections;  public class Move : MonoBehaviour {  // Use this for initialization void Start () {     ; }  // Update is called once per frame void Update () {     rigidbody2D.AddForce (Vector2.right * 10);     }  public void Groundand(Collider2D coll){     if (coll.gameObject.name == "ground") {         rigidbody2D.velocity = transform.up * 10;     }   }  }