Who's more likely to be the father

No judgment please. My last period started July 17 and ended the 22nd. My ex and I had sex July 23rd. We broke up and like a idiot I had sex aug 1st with a diff ex. I just found out today that I'm pregnant according to this app I ovulated around the 1st so does that completely X out guy number one or should I not rely on the app??

Edit to add. Yes I took a test today. And my cycles are anywhere between 26-28 days. No I wasn't tracking ovulation.