GetButtonDown not working

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class followMouse : MonoBehaviour
6. {
7.     public Transform firePoint;
8.     public GameObject bulletPrefab;
9.     public float bulletForce = 20;
10.     public float offset;
11.     private void Update()
12.     {
13.         Vector3 difference = Camera.main.ScreenToWorldPoint(Input.mousePosition) - transform.position;
14.         float rotZ = Mathf.Atan2(difference.y, difference.x) * Mathf.Rad2Deg;
15.         transform.rotation = Quaternion.Euler(0f, 0f, rotZ + offset);
16.         if (GetButtonDown("Fire1"))
17.         {
18.             Shoot();
19.         }
20.     }
21.     void Shoot()
22.     {
23.         Instatiate(bulletPrefab, firePoint.position, firePoint.rotation);
24.     }
25. }
26.  

 

Assets\followMouse.cs(16,13): error CS0103: The name 'GetButtonDown' does not exist in the current context

 

Did you mean Input.GetButtonDown?