#include <bits/stdc++.h>
#include <unistd.h>

using namespace std;

#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}


typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const ll MOD = 1000000007;
//const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { -1,0, 1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
// #define mp make_pair
//#define endl '\n'

/*
#define N 3010
#define M 5010
struct edge { ll from, to, cost; };
vector<edge> es(M);

vl d(N,INF);
ll n, m;

vii G(N);
vi is_reach(N, -1);
vi used(N);


//trueを返す場合、頂点以上に更新チェック→負のコストの閉ループあり
bool bellman_ford(ll s) {
	d[s] = 0;
	ll cnt = 0;
	bool updateFlag;
    int i = 0;
	while (true) {
		updateFlag = false;
		for (i = 0; i < m; i++) {
			if (d[es[i].from] != INF && d[es[i].to] > d[es[i].from] + es[i].cost) {
              if (not is_reach[es[i].to]) continue;
              d[es[i].to] = d[es[i].from] + es[i].cost;
              updateFlag = true;
			}
		}

		if (cnt == n - 1) return true;
		if (!updateFlag) break;

		cnt += 1;
	}
	return false;
}


bool dfs(int now) {
  if (is_reach[now] != -1) {
    return is_reach[now];
  }
  used[now] = true;
  bool flag = false;
  rep (i, G[now].size()) {
    int ch = G[now][i];
    if (used[ch]) {
      if (is_reach[ch] != -1) {
        return is_reach[ch];
      }
    }
    else {
      flag |= dfs(ch);
    }
  }
  is_reach[now] = flag;
  return is_reach[now];
}

int main() {
  int p;
  cin >> n >> m >> p;
  
  rep (i, m) {
    int u, v, c;
    cin >> u >> v >> c;
    u--; v--;
    es[i].from = u;
    es[i].to = v;
    es[i].cost = -(c - p);
    G[u].push_back(v);
    G[v].push_back(u);
  }

  is_reach[n - 1] = 1;
  rep (i, n) {
    if (is_reach[i] == -1) {
      dfs(i);
    }
  }

  if (bellman_ford(0)) {
    cout << -1 << endl;
  }
  else {
    cout << max(0LL, -d[n - 1]) << endl;
  }
}
//*/

int main() {
  int n, m;
  cin >> n >> m;
  vector<pii> ab(n);
  
  rep (i, n) {
    cin >> ab[i].first >> ab[i].second;
  }

  sort(all(ab));
  multiset<int, greater<int>> st;
  int j = 0;
  ll ans = 0;
  rrep (i, m) {
    while (j < n and ab[j].first + i <= m) {
      st.insert(ab[j].second);
      j++;
    }
    if (st.size()) {
      ans += *st.begin();
      st.erase(st.begin());
    }
  }
  cout << ans << endl;
}


Measured memory_bytes: 5632