class Heap
  attr_reader :size

  def initialize
    @heap = []
    @size = 0
  end

  def add(n)
    i = @size
    while i > 0 do
      parent_index = (i - 1) / 2
      break if n < @heap[parent_index]

      @heap[i] = @heap[parent_index]
      i = parent_index
    end

    @heap[i] = n
    @size += 1
  end

  def pop
    return if @size <= 0
    min_n = @heap[0]
    @size -= 1
    n = @heap[@size]
    i = 0
    while i * 2 + 1 < @size do
      child_index1 = i * 2 + 1
      child_index2 = i * 2 + 2
      if child_index2 < @size && @heap[child_index2] >= @heap[child_index1]
        child_index1 = child_index2
      end
      break if @heap[child_index1] < n

      @heap[i] = @heap[child_index1]
      i = child_index1
    end
    @heap[i] = n
    min_n
  end

  def min; @heap[0] end
  def values; @heap.first(@size) end
  def inspect; "Heap: #{values}" end
end


N, M = gets.split.map!(&:to_i)
A = 0
B = 1
ab = {}
N.times.map do
  a, b = gets.split.map(&:to_i)
  ab[a] ||= []
  ab[a] << b
end

heap = Heap.new
ans = 0
1.upto(M) do |m|
  ab[m].each { |c| heap.add(c) } if ab[m]
  top = heap.pop()
  ans += top if top
end

puts ans