In Reply 1988, who is the main male lead?

Who is the main male lead in this show? Clearly the main girl is Hyeri as she's the only girl with "main role". For the guys, there's 4 of them, which one is it?

Unlike the other two Reply series, romance is less of a focus in Reply 1988 .Yeah there is romance but the story mainly focuses more on the family moments, friendship, childhood & the neighborhood. So all the characters including the parents  had important roles to play. 

& what's the definition of a "male lead" ?  the one who had more screentime or the one with whom the female lead ends up with ? it's hard to answer this question, right ?

If by main lead you mean  the one the girl chooses, that's a spoiler.  If you mean the one who gets the most focus, the most popular opinion is Ryu Jun Yeol's character. Although I'd argue that Go Kyung  Pyo's character had an equal amount of it.