Write a program to print a calendar.
You will have a year, a month, and the day of the first of the month.
Then you need to print a calendar for that month.
Note that you need to determine if the given year is a leap year when it is February.
The input has three numbers: year, month, and the day of the first day of that month.
For example, if you have 2007 9 6, it means you need to print out a calendar of September 2007, with the additional information that the first day of September is a Saturday.
If the day is $0$, it means Sunday.
We ensure that the year is between $1000$ and $3000$ inclusively.
The output is a calendar of that month.
First line is Su Mo Tu We Th Fr Sa\n to indicate the days. Then every number will be printed as %3d -- the 3 indicates the width of the number, and the numbers are enclosed by two =====================\n.
Note that you cannot put trailing spaces at the end of each line, nor put extra \n at the end of the output.
Also, note that if the input is not valid, such as 2007 13 9, print an invalid\n.