local mfl = math.floor
local n = io.read("*n")
local asum = 0
local a = {}
for i = 1, n do
  a[i] = io.read("*n")
end
for i = 1, n do
  local bi = io.read("*n")
  a[i] = a[i] - bi
  asum = asum + a[i]
end
if n == 2 then
  if asum == 0 then
    print(math.abs(a[1]))
  else
    print(-1)
  end
  os.exit()
end
if asum == 0 then
  local allsame = true
  for i = 1, n do
    if a[i] ~= 0 then allsame = false break end
  end
  if not allsame then
    print(-1)
  else
    print(0)
  end
  os.exit()
end
if asum <= 0 then
  print(-1)
  os.exit()
end
if asum % (n - 2) ~= 0 then
  print(-1)
  os.exit()
end
local cnt = mfl(asum / (n - 2))
for i = 1, n do
  a[i] = a[i] - cnt
  if 0 < a[i] then print(-1) os.exit() end
  a[i] = -a[i]
  if a[i] % 2 == 1 then
    print(-1) os.exit()
  end
end
print(cnt)