import itertools

while True:

    N = int(eval(input()))

    if not N:

        break

    D = [[] for _ in range(30)]

    for i in range(N):

        for x in map(int, input().split()[1:]):

            D[x - 1].append(i)

    C = [1 << i for i in range(N)]

    for d in range(30):

        for i, j in itertools.permutations(D[d], 2):

            C[i] = C[i] | C[j]

        if any(x == (1 << N) - 1 for x in C):

            print((d + 1))

            break

    else:

        print((-1))
import itertools

while True:

    N = int(eval(input()))

    if not N:

        break

    D = [[] for _ in range(30)]

    for i in range(N):

        for x in map(int, input().split()[1:]):

            D[x - 1].append(i)

    C = [1 << i for i in range(N)]

    for d in range(30):

        for i, j in itertools.combinations(D[d], 2):

            C[i] = C[j] = C[i] | C[j]

        if any(x == (1 << N) - 1 for x in C):

            print((d + 1))

            break

    else:

        print((-1))
import itertools

while True:
    N = int(eval(input()))
    if not N:
        break
    D = [[] for _ in range(30)]
    for i in range(N):
        for x in map(int, input().split()[1:]):
            D[x - 1].append(i)
    C = [1 << i for i in range(N)]
    for d in range(30):
        for i, j in itertools.permutations(D[d], 2):
            C[i] = C[i] | C[j]
        if any(x == (1 << N) - 1 for x in C):
            print((d + 1))
            break
    else:
        print((-1))

import itertools

while True:
    N = int(eval(input()))
    if not N:
        break
    D = [[] for _ in range(30)]
    for i in range(N):
        for x in map(int, input().split()[1:]):
            D[x - 1].append(i)
    C = [1 << i for i in range(N)]
    for d in range(30):
        for i, j in itertools.combinations(D[d], 2):
            C[i] = C[j] = C[i] | C[j]
        if any(x == (1 << N) - 1 for x in C):
            print((d + 1))
            break
    else:
        print((-1))

-        for i, j in itertools.permutations(D[d], 2): -            C[i] = C[i] | C[j] +        for i, j in itertools.combinations(D[d], 2): +            C[i] = C[j] = C[i] | C[j]