class Solution(object):
    def keyboard(self,words):
        row1 = set('qwertyuiop')
        row2 = set('asdfghjkl')
		row3 = set('zxcvbnm')
		out = []

		for word in words:
		    inp = set(word.lower())
			for ref in [row1, row2, row3]:
			    if inp & ref == inp:
				    out.append(word)
					break

		return out