n = int(input())
a = list(map(int, input().split()))
b = list(map(int, input().split()))

sa = sum(a)
sb = sum(b)

if n == 2:
  if sa != sb:
    print("-1")
  else:
    print(abs(a[0] - b[0]))
  exit()

if sa - sb < 0 or (sa - sb) % (n - 2) != 0:
  print("-1")
  exit()

cnt = (sa - sb) // (n - 2)
rest = cnt
for i in range(n):
  a[i] -= cnt
  if a[i] > b[i]:
    print("-1")
    exit()
  else:
    cost = min(rest, (b[i] - a[i]) // 2)
    a[i] += 2 * cost
    rest -= cost

if a == b:
  print(cnt)
else:
  print("-1")