'''
Given a string s consisting of small English letters, find and return the first instance of a non-repeating character in it. 

If there is no such character, return '_'.
'''

def solution(s):
    return '_'


print(solution("abacabaabacaba")
     ) #output "_"

print(solution("abacabad")
     ) #output "c"

print(solution("bcccccccccccccyb")) #output "y"