How to do one jump in unity?

Question

Unity

I made a script for the main character, but if you press the spacebar all the time, then he flies out of the map, how to make a single jump? Here is the script.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class perss : MonoBehavior {

Rigidbody2D rb;

void Start() {

rb = GetComponent();
}

void Update () {
if (Input.GetKeyDown (KeyCode.Space)) {
pipirka ();
}
}

void FixedUpdate () {

rb.velocity = new Vector2(Input.GetAxis("Horizontal") * 9f, rb.velocity.y);
}

void pipirka(){

rb.AddForce(transform.up * 7f, ForceMode2D.Impulse);
}

void Reload(){
Application.LoadLevel(Application.loadedLevel);
}
}