I want get, how much month have got days. I have got this code:

```
    Calendar cal = Calendar.getInstance();
    cal.set(2013, 1, 1);
    System.out.println(cal.getActualMaximum(cal.DAY_OF_MONTH));

```

Januar of year 2013 (and other else yaers :)) have got 31 days, but, I'm still getting 28, do you know, where I have got mistake? 
Thank you.