Problem F. Four Cards

#ACM ICPC 2016/2017
class card:
    def __init__(self,rank,suit):
        self.rank=rank
        self.suit=suit
mas=[]
for l in input().split(" ")[1:]:
    mas.append(card(l[0],l[1]))
i=0
p=1
while i<len(mas)-1:
    if p==0:break
    j=i+1
    while j<len(mas):
        if mas[i].rank==mas[j].rank:
            mas[i+1],mas[j]=mas[j],mas[i+1]
            break
        elif mas[i].suit==mas[j].suit:
            mas[i+1],mas[j]=mas[j],mas[i+1]
            break
        j+=1
    else:
        print("NO")
        p=0
        break

    i+=1
else:
    print("YES")