def solution(x, y):
    p, q = (sorted(x), sorted(y)) if len(x) > len(y) else (sorted(y), sorted(x))
    for i, v in enumerate(p):
        if v != q[i]:
            return v

tests = [
        ([[13, 5, 6, 2, 5], [5, 2, 5, 13]], 6),
        ([[14, 27, 1, 4, 2, 50, 3, 1], [2, 4, -4, 3, 1, 1, 14, 27, 50]], -4),
        ]

for i, o in tests:
    result = solution(*i)
    print (i, result == o, result, o)