Alex Maximovich

<uses-permission android:name="com.android.vending.BILLING" />

public class Coins : MonoBehaviour
{
  public Text text;
  private int coins;

  void Start () {
    coins = PlayerPrefs.GetInt("coins", 0);
    text.text = coins.ToString();
  }
  public int Coins {
  get {return coins;}
  set {
      coins = value;
      text.text = coins.ToString();
      PlayerPrefs.SetInt("coins", coins);
      PlayerPrefs.Save();
  }
 }

}

private int _timeLeft = 5;
public Text countdownText;
private float _currentTime;

void Start()
{
    _currentTime = _timeLeft;
}

void Update()
{
    _currentTime -= Time.deltaTime;   
    countdownText.text = (int)_currentTime.ToString());    
    if(_currentTime <= 0)    
    {
        Debug.Log("StartGame");
    }
}