import numpy as np

N = int(input())
A = np.array(input().split(), dtype=np.int64)
B = np.array(input().split(), dtype=np.int64)

ans = -1
v = (A.sum() - B.sum()) / (N - 2)

if ((B - A + v) % 2 == 0).all() and ((B - A + v) / 2).sum() == v:
    ans = int(v)

print(ans)