N = int(input())
A = [input() for _ in range(N)]
M = int(input())
B = [input() for _ in range(M)]

for i in range(N):
    for j in range(M):
        if A[i][0] == B[j][0]:
            str0, str1 = A.pop(i), B.pop(j)
            break
    else:
        continue
    break

while True:
    if str0 == str1:
        if len(A) == 0 and len(B) == 0:
            print(str0)
        else:
            print(-1)
        break
    
    if len(str0) > len(str1):
        for i in range(len(B)):
            if B[i][0] == str0[len(str1)]:
                str1 += B.pop(i)
                break
    else:
        for i in range(len(A)):
            if A[i][0] == str1[len(str0)]:
                str0 += A.pop(i)
                break