n= int(input())
response = {input() for line in range(n)}
NO = {i for i in response if i[-2:] == "NO"}
y = tuple(map(lambda s: "".join([c for c in s if c.isdigit()]), response - NO))
YES = set("".join(map(lambda i: i if all([(i in r) for r in y]) else "", y[0])))
print("".join((YES if len(YES) > 0 else set("0123456789")) - set("".join(NO))))