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]
  (m + x%m) % m
end

def lc(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
    t = b/d * mod_inv(a/d, ms[i]/d) % (ms[i]/d)
    x = x + m*t
    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

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