n, m = read_line.split.map(&.to_i)
d = Array.new(n) do
  a, b = read_line.split.map(&.to_i)
  (m + 1 - a + b - 1) // b
end.sort
lo = 0
hi = 1_000_000_000
while hi - lo > 1
  mid = (lo + hi) // 2
  if n.times.all? { |i| d[i] > i // mid }
    hi = mid
  else
    lo = mid
  end
end
puts hi