5. In a certain social event, it was originally planned that every two people would shake hands exactly once, but after 4 people each shook hands twice they left. As a result, a total of 60 handshakes took place throughout the event. How many people initially attended the event? $\qquad$ .
Let 4 people shake hands $x$ times, then we have $C_{n-4}^{2}+8-2 x+x=60 \Rightarrow n=15, x=3$.