# 嘘解法の提出。WA になるべき。
import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

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

def main(A, B):
    N = len(A)
    SA, SB = A.sum(), B.sum()
    if N == 2:
        if SA != SB:
            return -1
        return np.abs(A - B).sum() // 2
    K = (SA - SB) // (N - 2)
    A -= K
    x = B - A
    # if np.all((x >= 0) & (x % 2 == 0)):
    if np.all(x >= 0):
        return K
    else:
        return -1

print(main(A, B))