class PriorityQueue
  def initialize(array = [])
    @data = []
    array.each{|a| push(a)}
  end

  def push(element)
    @data.push(element)
    bottom_up
  end

  def pop
    if size == 0
      return nil
    elsif size == 1
      return @data.pop
    else
      min = @data[0]
      @data[0] = @data.pop
      top_down
      return min
    end
  end

  private

  def swap(i, j)
    @data[i], @data[j] = @data[j], @data[i]
  end

  def size
    @data.size
  end

  def parent_idx(target_idx)
    (target_idx - (target_idx.even? ? 2 : 1)) / 2
  end

  def bottom_up
    target_idx = size - 1
    return if target_idx == 0
    parent_idx = parent_idx(target_idx)
    while (@data[parent_idx] > @data[target_idx])
      swap(parent_idx, target_idx)
      target_idx = parent_idx
      break if target_idx == 0
      parent_idx = parent_idx(target_idx)
    end
  end

  def top_down
    target_idx = 0

    # child がある場合
    while (has_child?(target_idx))

      a = left_child_idx(target_idx)
      b = right_child_idx(target_idx)

      if @data[b].nil?
        c = a
      else
        c = @data[a] <= @data[b] ? a : b
      end

      if @data[target_idx] > @data[c]
        swap(target_idx, c)
        target_idx = c
      else
        return
      end
    end
  end

  # @param Integer
  # @return Integer
  def left_child_idx(idx)
    (idx * 2) + 1
  end

  # @param Integer
  # @return Integer
  def right_child_idx(idx)
    (idx * 2) + 2
  end

  # @param Integer
  # @return Boolent
  def has_child?(idx)
    ((idx * 2) + 1) < @data.size
  end
end



# class PriorityQueue
#   attr_accessor :data, :size
 
#   def initialize(array = [])
#     @data = []
#     array.each { |a| push(a) }
#   end
 
#   def push(element)
#     current = @data.size
#     while current > 0
#       p = parent(current)
#       break if @data[p] <= element
#       @data[current] = @data[p]
#       current = p
#     end
#     @data[current] = element
#   end
 
#   def pop
#     ret = @data[0]
#     x = @data[-1]
#     current = 0
#     while have_child?(current)
#       a = left_child(current)
#       b = right_child(current)
#       a = b if b < @data.size - 1 && @data[b] <= @data[a]
#       break if @data[a] >= x
#       @data[current] = @data[a]
#       current = a
#     end
#     @data[current] = x
#     @data.pop
 
#     ret
#   end
 
#   def size
#     @data.size
#   end
 
#   def front
#     @data[0]
#   end
 
#   def empty?
#     @data.empty?
#   end
 
#   private
#   def parent(num)
#     (num - 1) / 2
#   end
 
#   def left_child(num)
#     num * 2 + 1
#   end
 
#   def right_child(num)
#     num * 2 + 2
#   end
 
#   def have_child?(num)
#     left_child(num) < @data.size - 1
#   end
# end


N, M = gets.chomp.split(' ').map(&:to_i)

AB = []
N.times do |i|
  AB[i] = gets.chomp.split(' ').map(&:to_i)
end

group_by_day = Hash[AB.group_by{|v|v[0]}.sort]

day_fee = Array.new(M){[]}
group_by_day.each do |k,v|
  day_fee[k-1] = v.map{|j| j[1]}
end

# require 'pry'
# binding.pry

ans = 0
pq = PriorityQueue.new
day_fee.each_with_index do |fees, idx|
  break if idx > M - 1
  fees.each do |fee|
    pq.push(fee*(-1))
  end
  ans += pq.pop.to_i
  # p pq
  # p pq.pop*(-1)
end

puts ans*(-1)


Measured memory_bytes: 38284