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 lc(a,b,m)
  xx,mm = 0,1
  a.size.times do |i|
    aa = a[i]*mm
    bb = b[i] - a[i] * xx
    dd = m[i].gcd(aa)
    return if bb % dd != 0
    tt = bb/dd * mod_inv(aa/dd, m[i]/dd) % (m[i] / dd)
    xx = xx + mm*tt
    mm *= m[i]/dd
  end
  return [xx%mm,mm]
end

n = gets.to_i

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

as = [1] * n

ans = lc(as,xs,ys)
puts ans.nil? ? -1 : ((ans[0] == 0 ? ans[1] : ans[0])) % 1000000007