#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rrep(i,n) for(int (i)=((n)-1);(i)>=0;(i)--)
#define itn int
#define all(x) (x).begin(),(x).end()
#define F first
#define S second
using P = pair <int,int>; //to, cost
using WeightedGraph = vector<vector <P>>; //to cost
const long long INF = 1LL << 60;
const int MOD = 1000000007;
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
//https://www.creativ.xyz/dump-cpp-652/
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
 
// vector
template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec) is >> x;
    return is;
}
// pair
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
    os << "(" << pair_var.first << ", " << pair_var.second << ")";
    return os;
}
// vector
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &vec) {
    os << "{";
    for (int i = 0; i < vec.size(); i++) {
        os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
    }
    os << "}";
    return os;
}
// map
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
    os << "{";
    repi(itr, map_var) {
        os << *itr;
        itr++;
        if (itr != map_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}
// set
template <typename T>
ostream &operator<<(ostream &os, set<T> &set_var) {
    os << "{";
    repi(itr, set_var) {
        os << *itr;
        itr++;
        if (itr != set_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}
 
#define DUMPOUT cerr
 
void dump_func() {
    DUMPOUT << endl;
}
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&... tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) > 0) {
        DUMPOUT << ", ";
    }
    dump_func(std::move(tail)...);
}

#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \
    DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                            \
            << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]"        \
            << endl                                                            \
            << "    ",                                                         \
        dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif
struct SegTree{
    int n;
    vector <pair <int,int> > node;
    SegTree(vector <int> v){
        int sz = v.size();
        n = 1;
        while(n<sz) n*=2;
        node.resize(2*n-1, {0,-INF});
        for(int i=0; i<sz; i++) node[i+n-1] = {v[i],i}; //一番下側
        for(int i=n-2;i>=0;i--) node[i] = max(node[2*i+1], node[2*i+2]);
    }
    int getnum(int p){
        return node[n-1+p].F;
    }
    int geti(int p){
        return node[n-1+p].S;
    }
    void update(int number, int val){
        number += n-1;
        node[number].F= val;
        while(number>0){
            number=(number-1)/2;
            node[number] = max(node[number*2+1], node[number*2+2]);
        }
    }
    pair <int,int> getmax(int a, int b, int k=0, int l = 0, int r = -1){ //0~n
        //値と場所
        if(r<0) r=n;
        if(r<=a||b<=l) return {0,-INF};
        if(a <= l&& r<=b) return node[k];
        pair <int,int>  vl = getmax(a, b, 2*k+1, l, (l+r)/2);
        pair <int,int>  vr = getmax(a, b, 2*k+2, (l+r)/2, r);
        return max(vl, vr);
    }
    void showall(){
        for(int i=0;i<2*n-1;i++)cout<<node[i].F<<'&'<<node[i].S<<endl;
    }
};
//http://tsutaj.hatenablog.com/entry/2017/03/30/224339
signed main(void) { cin.tie(0); ios::sync_with_stdio(false);
    int n,m; cin>>n>>m;
    vector <pair<int,int>> p(n);
 
    rep(i,n){
        int a,b; cin>>a>>b;
        p[i] = {a,b};
    }
    sort(p.begin(),p.end());
    priority_queue <int> pq;
    

    int x = 0, days = 0;
    int ans = 0;
    for(int i=0;i<=m;i++){
        if(x < n){
            while(p[x].F <= i){
                //cout<<"push"<<' '<<p[x].S<<endl;
                pq.push(p[x].S);
                x++;
                if(x>= n) break;
            }
            
        }
        if(!pq.empty()){
            ans += pq.top();
            pq.pop();
        }
        //cout<<i<<' '<<ans<<endl;
    }
    cout<<ans<<endl;
}


Measured memory_bytes: 2936