N = gets.to_i
A = gets.split.map(&:to_i)
B = gets.split.map(&:to_i)
S_A = A.sum
S_B = B.sum

if N == 2
  if S_A == S_B
    puts (A[0] - B[0]).abs
  else
    puts -1
  end
else
  if S_A >= S_B && (S_A - S_B) % (N - 2) == 0
    v = (S_A - S_B) / (N - 2)
    P = A.zip(B).map { |a, b| b - (a - v) }

    if P.all? { |x| x >= 0 && x.even? } && P.sum == 2 * v
      puts v
    else
      puts -1
    end
  else
    puts -1
  end
end