Remark
I'm just going to eave a very short note and if you answer quickly in the comments, I'll come back and edit the question.
Argument
If consists of 2 sides and 2 semicircles. Without a width, there is no number to be given. We can get a formula
Fomula
Perimeter = 2*sides + 2pi *w/2
Perimeter = 2*13 + pi*W