No. 1: 1+7- 1 = 7
Week 2:1+14-1=13
Week 3:1+21-1= 21
Week 4: 1+28- 1 = 28.
If it is Wednesday, the calculation is as follows:
3+7- 1=9
3+ 14- 1= 16
3+2 1- 1=23
3+28- 1=30
That is, the day of the week plus the number of weeks of the week *2 minus 1 is the date of this month. (If the first week of this month is less than one week, subtract 1 instead of 7.