Whose the father?

I just want to try to oblige my friend..! She have deeply irregular menstration. Her period ultimate on 19 of june and he have sex next to her bf 23-30, and she have sex to other guy 1-6 of july..! And in a minute she's pregnant, who do you think the father..? I'm thinking the july guy. If she did it near the first dude 3-10 days after her period consequently that guy couldn't have gotten her pregnant all right not couldn't he just have less probability of being the father
Its concrete to say. The date of her sexual encounters are to close to report to. The only instrument to determine the father is a DNA test.