n = gets.to_i
a = gets.split.map &:to_i
b = gets.split.map &:to_i

if n == 2
	puts (a[0] - b[0]) == (b[1] - a[1]) ? (a[0] - b[0]).abs : -1
	exit
end

minus = a.sum - b.sum
if minus % (n - 2) != 0
	puts -1
	exit
end
cnt = minus / (n - 2)
a = a.map { |i| i -= cnt }
if (0...n).any? { |i| a[i] > b[i] || (b[i] - a[i]) % 2 == 1 }
	puts -1
	exit
end

puts (0...n).sum { |i| (b[i] - a[i]) / 2 } == cnt ? cnt : -1