Could I contract HIV from the blood?

While in town today, I witnessed a tramp being beaten up, me and my friends ran over to him, the guy beating him had already ran away. He refused our help and our offer to call an ambulance but asked for a tissue. When he took the tissue from me a smear of blood was left on my hand, without thinking about it, I licked another finger, rubbed at the blood, licked again and rubbed again. It was only after that I realized this man could have been a heroin user and I could contract HIV/Aids! I am not trying to be prejudice towards him or his situation but I am feeling very worried. The blood was on my hand for at least a minute and I have no cuts in my mouth or on my hands. I was just wondering if anyone would be able to advice me? Thankss!