What to wear to a maths seminar?

I'm going to another city to my first maths seminar. While I've been at colloquia in campus, consisting mostly of lectures given by our professors' fields of study, this one's more advanced and will have people coming over from different countries. Out of respect for the speakers, I'm inclined to wear pants (anything but denim) and sweaters or buttoned shirts with any shoes other than tennis shoes. However, I'll go for jeans with plain t-shirts and tennis shoes for the sake of comfort if it's ok to do so. Any advice?