#include <bits/stdc++.h>
using namespace std;

#define repr(i, a, b) for (int i = (a), i##_len = (b); i < i##_len; ++i)
#define rep(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define irepr(i, a, b) for (int i = (a), i##_len = (b); i >= i##_len; --i)
#define irep(i, n) for (int i = (n), i >= 0; --i)

#define all(arr) begin(arr), end(arr)

#define printline(str) cout << str << "\n"

#define lint long long
#define ulint unsigned long long

#define pii pair<int, int>

ostream& operator<<(ostream& os, const pii& p){
  os << "[" << p.first << "," << p.second << "]";
  return os;
}

template <class T>
void printArray(const T &arr, string del = string(", "))
{
  for (auto it = begin(arr); it != end(arr); it++)
  {
    cout << (it != cbegin(arr) ? del : "") << *it;
  }
  cout << "\n";
}

constexpr char delimiter[] = " ";

void print() {
  cout << endl;
}

template <class Head, class... Tail>
void print(Head&& head, Tail&&... tail) {
  cout << head;
  if (sizeof...(tail) != 0) cout << delimiter;
  print(forward<Tail>(tail)...);
}

template <class T>
void print(vector<T> &vec) {
  for (auto& a : vec) {
    cout << a;
    if (&a != &vec.back()) cout << delimiter;
  }
  cout << endl;
}

template <class T, class U>
void print(multiset<T, U> &vec) {
  for( auto it = begin(vec); it != end(vec);  ++it){
    if (it != begin(vec)) cout << delimiter;
    cout << *it;
  }
  cout << endl;
}

template <class T>
void print(vector<vector<T>> &df) {
  for (auto& vec : df) {
    print(vec);
  }
}


class BIT
{
private:
  int n;
  vector<int> nodes;

public:
  BIT(vector<int> v)
  {
    int size = v.size();
    n = 1;
    while (n < size)
    {
      n *= 2;
    }
    nodes.resize(n, 0);
    rep(i, size)
    {
      add(i, v[i]);
    }
  }

  void add(int i, int val)
  {
    ++i;
    while (i <= n)
    {
      nodes[i] += val;
      i += i & -i;
    }
  }

  int sum(int i)
  {
    ++i;
    int ret = 0;
    while (i > 0)
    {
      ret += nodes[i];
      i -= i & -i;
    }
    return ret;
  }
};

struct UnionFindTree
{
  // 自身の親ノードのインデックスを表す
  // 自身が親の場合はぶら下がってるノードの総数を表す
  vector<int> nodes;

  UnionFindTree(int N) : nodes(N, -1)
  {
  }
  
  int Root(int i ){
    if( nodes[i] < 0){
      return i;
    }
    return nodes[i] = Root(nodes[i]);
  }

  bool Connect(int i, int j){
    auto rootI = Root(i);
    auto rootJ = Root(j);
    if( rootI == rootJ){
      return false;
    }
    nodes[rootI] += nodes[rootJ];
    nodes[rootJ] = rootI;
    return true;
  }

};

class RollingHash
{
private:
  static constexpr int modNum = 2;
  const array<lint, modNum> mod = {{999999937LL, 1000000007LL}};
  static const lint base = 9973;
  vector<lint> pw[modNum];
  RollingHash() {}

public:
  int size;
  vector<lint> hs[modNum];

  RollingHash(const string &s)
  {
    size = s.size();
    for (int i = 0; i < modNum; i++)
    {
      hs[i].assign(size + 1, 0);
      pw[i].assign(size + 1, 0);
      hs[i][0] = 0;
      pw[i][0] = 1;
      for (int j = 0; j < size; j++)
      {
        pw[i][j + 1] = pw[i][j] * base % mod[i];
        hs[i][j + 1] = (hs[i][j] * base + s[j]) % mod[i];
      }
    }
  }

  lint Hash(int l, int r, int i)
  {
    return ((hs[i][r] - hs[i][l] * pw[i][r - l]) % mod[i] + mod[i]) % mod[i];
  }

  array<lint, modNum> Hash(int l, int r){
    array<lint, modNum> ret;
    rep(i, modNum)
      ret[i] = Hash(l, r, i);
    return ret;
  }

  bool Match(int l1, int r1, int l2, int r2)
  {
    bool ret = 1;
    for (int i = 0; i < modNum; i++)
      ret &= Hash(l1, r1, i) == Hash(l2, r2, i);
    return ret;
  }

  bool Match(int l, int r, array<lint, modNum> h)
  {
    bool ret = 1;
    for (int i = 0; i < modNum; i++)
      ret &= Hash(l, r, i) == h[i];
    return ret;
  }
};



int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int N, M;
  cin >> N >> M;

  vector<vector<int>> works(M+1);

  rep(i,N){
    int A, B;
    cin >> A >> B;
    if( A <= M){
      works[A].push_back(B);
    }
  }


  priority_queue<int> w;
  ulint s = 0;
  repr(i, 1, M+1){
    rep(j, works[i].size())
      w.push(works[i][j]);
    
    if( w.empty())
      continue;
    s += w.top();
    w.pop();;
  }

  print(s);
}

Measured memory_bytes: 5632