def extgcd(a, b)
  if b.zero?
    {x: 1, y: 0, gcd: a}
  else
    prev = extgcd(b, a % b)
    {
      x: prev[:y],
      y: prev[:x] - (a / b) * prev[:y],
      gcd: prev[:gcd]
    }
  end
end

def mod_inv(a,m)
  res = extgcd(a,m)
  x = res[:x]
  return (m+x%m)%m
end

def linear_congruence(as,bs,ms)
  x,m = 0,1
  as.size.times do |i|
    a = as[i]*m
    b = bs[i] - as[i] * x
    d = ms[i].gcd(a)
    return if b % d != 0
    tt = b/d * mod_inv(a/d, ms[i]/d) % (ms[i]/d)
    x = x + m*tt
    m *= ms[i]/d
  end
  return [x%m, m]
end

n = gets.to_i
t = []
n.times do
  x,y = gets.chomp.split.map(&:to_i)
  t << [x,y]
end
xs,ys = t.transpose

as = [1] * n

mod = 1000000007
ans = linear_congruence(as,xs,ys)
puts ->(x){
  if x.nil?
    -1
  elsif ans[0] == 0
    ans[1] % mod
  else
    ans[0] % mod
  end
}.call(ans)