I think the task could be even more clearer. I understand the task as if there could be many smiles in one String, so I've been writing code to count smiles for input String like :-)k :D ;] hello:)

There is no mention of any symbols except for mouth, nose, and eyes so :-)k is not a valid smiley face according to the rules.
Anyway just to be sure there is no missconfusion I added to description No additional characters are allowed except for those mentioned.