n = int(input())
l = []
s1 = set()
s2 = set()
for i in range(n):
    l += [input().split()]
    if l[i][-1] == "NO":
        s1 |= set(l[i])
    else:
        if len(s2) == 0:
            s2 = set(l[i])
        else:
            s3 = s2 | set(l[i])
            s2 &= set(l[i])
            s1 |= set([x for x in s3 if x not in s2])
if len(s2) > 1:
    s2.remove("YES")
a=""
for i in s2:
    if i not in s1:
        a = i
if a == "":
    for i in range(10):
        if str(i) not in s1:
            a = i
print(a)