Help me to fix my script error cs1519

hello im following a tutorial but i have a problem at this point and i dont know where is the prob :(

Assets/Scripts/TileManager.cs(17,67): error CS1519: Unexpected symbol `(' in class, struct, or interface member declaration

using UnityEngine; using System.Collections;

public class TileManager : MonoBehaviour {

 public GameObject[] tilePrefabs;

 public GameObject currentTile;

 private static TileManager instance;


 private Stack<GameObject> leftTiles - new Stack<GameObject>();

 private Stack<GameObject> topTiles - new Stack<GameObject>();

 public static TileManager Instance
 {
     get
     {
         if (instance == null)
         {
             instance = GameObject.FindObjectOfType<TileManager>();
         }
         return instance;
     }
 }
 // Use this for initialization
 void Start () 
 {
     CreateTiles (100); 
     for (int i = 0; i < 3000; i++)
     {
         SpawnTile();
     }
 }
 
 // Update is called once per frame
 void Update () {
 
 }
 public void CreateTiles(int amount)
 {
     for (int i= 0; i < amount; i++)
     {
         leftTiles.Push(Instantiate(tilePrefabs[0])); 
         topTiles.Push(Instantiate(tilePrefabs[1])); 
         topTiles.Peek().SetActive(false);
         leftTiles.Peek().SetActive(false);
     }

 }
 public void SpawnTile()
 {
     if (lefTiles.Count == 0 || topTiles.Count == 0)
     {
         CreateTiles(10);
     }
     int spawnPickUp = Random.Range (0, 8);
     if (spawnPickUp == 0)
     {
         currentTile.transform.GetChild(1).gameObject.SetActive(true);
     }

         int randomIndex = Random.Range (0, 2);

     if (randomIndex == 0)
     {
         GameObject tmp = leftTiles.Pop();
         tmp.SetActive(true);
         tmp.transform.position = currentTile.transform.GetChild(0).transform.GetChild(randomIndex).position; 
         currentTile = tmp;
     }
     else if(randomIndex == 1)
     {
         GameObject tmp = topTiles.Pop();
         tmp.SetActive(true);
         tmp.transform.position = currentTile.transform.GetChild(0).transform.GetChild(randomIndex).position; 
         currentTile = tmp;
     }

     //currentTile = (GameObject)Instantiate (tilePrefabs[randomIndex], currentTile.transform.GetChild(0).transform.GetChild (randomIndex).position, Quaternion.identity);  
 }    

}