// Original C++ solution (slower):
#include<bits/stdc++.h>

using namespace std;



#define int long long

#define endl "\n"

#define REP(i,a,n) for(int i=a;i<n;++i)

#define REPR(i,a,n) for(int i=a;i>n;--i)

#define RUP(a,b) ((a+b-1)/(b))

#define ALL(v) (v).begin(),(v).end()

#define pb push_back

#define mp make_pair

#define mt make_tuple



typedef long long ll;

typedef pair<int,int> Pii;

typedef tuple<int,int,int> Tiii;

typedef vector<int> Vi;

typedef vector<Vi> VVi;

typedef vector<Pii> VPii;

typedef vector<string> Vs;



template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}

template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

template<class T> void YesNo(T a) {cout<<(a?"Yes":"No")<<endl;}

template<class T> void YESNO(T a) {cout<<(a?"YES":"NO")<<endl;}

int gcd(int a,int b){return b?gcd(b,a%b):a;}

int lcm(int a,int b){return a/gcd(a,b)*b;}

void uniq(Vi &v){sort(v.begin(),v.end()); v.erase(unique(v.begin(),v.end()),v.end());}

const int MOD=1000000007;

const int INF=LLONG_MAX/2;

const int Maxa=200000;





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

    int n,m,ans=0;

    cin>>n>>m;

    VVi a(Maxa);

    REP(i,0,n){

        int tmpa,tmpb;

        cin>>tmpa>>tmpb;

        a[tmpa].pb(tmpb);

    }

    

    multiset<int> se;

    REP(i,1,m+1){

        REP(j,0,a[i].size()){

            se.insert(a[i][j]);

        }

        if(se.size()!=0){

            auto itr=se.end();

            itr--;

            ans += *itr;

            se.erase(itr);

        }

    }

    cout<<ans<<endl;

    return 0;

}


// Optimized solution to the same problem (faster):
#include<bits/stdc++.h>

using namespace std;

//#include<boost/multiprecision/cpp_int.hpp>

//using boost::multiprecision::cpp_int;



#define int long long

#define cint cpp_int

#define endl "\n"

#define REP(i,a,n) for(int i=a;i<n;++i)

#define REPR(i,a,n) for(int i=a;i>n;--i)

#define RUP(a,b) (((a)+(b)-1)/(b))

#define ALL(v) (v).begin(),(v).end()

#define pb push_back

#define mp make_pair

#define mt make_tuple

#define MOD 1000000007

#define INF LLONG_MAX/2

#define PI acos(-1.0)



typedef long long ll;

typedef pair<int,int> Pii;

typedef tuple<int,int,int> Tiii;

typedef vector<int> Vi;

typedef vector<Vi> VVi;

typedef vector<Pii> VPii;

typedef vector<string> Vs;

typedef priority_queue<int> PQi;



template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}

template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

void vout(Vi &v){for(int i=0;i<(v).size();i++) cout<<v[i]<<" ";cout<<endl;}

void vout(Vs &v){for(int i=0;i<(v).size();i++) cout<<v[i]<<" ";cout<<endl;}

void vvout(VVi &v){for(int i=0;i<(v).size();i++) vout(v[i]);}

int gcd(int a,int b){return b?gcd(b,a%b):a;}

int lcm(int a,int b){return a/gcd(a,b)*b;}

int mypow(int x, int n, int m){if(n==0)return 1;if(n%2==0)return mypow(x*x%m,n/2,m);else return x*mypow(x,n-1,m)%m;}

int digit(int k,int i){string s = to_string(k);return s[s.size()-i]-'0';}

void uniq(Vi &v){sort(v.begin(),v.end()); v.erase(unique(v.begin(),v.end()),v.end());} //vectorの同じ要素消す

int ctoi(char c){if(c>='0'&&c<='9'){return c-'0';}return 0;}

int leng(int n){string s=to_string(n); return s.size();} //intの桁数

int digitsum(int n){int ret=0; while(n>0){ret+=n%10;n/=10;}return ret;} //桁和

int lesscount(int x,Vi &a){return lower_bound(a.begin(),a.end(),x)-a.begin();} //vector aにおけるx未満の数の個数

int orlesscount(int x,Vi &a){return upper_bound(a.begin(),a.end(),x)-a.begin();} //vector aにおけるx以下の数の個数

int morecount(int x,Vi &a){return a.size()-orlesscount(x,a);} //vector aにおけるxより大きい数の個数

int ormorecount(int x,Vi &a){return a.size()-lesscount(x,a);} //vector aにおけるx以上の数の個数

int count(int x,Vi &a) {return upper_bound(ALL(a),x)-lower_bound(ALL(a),x);} //vector aにおけるxの個数

Vi accum(Vi &v){Vi ret((v).size()+1);REP(i,0,(v).size()) ret[i+1]=ret[i]+v[i];return ret;}

bool comp(Pii a,Pii b){

    if(a.second != b.second) return a.second<b.second;

    else return a.first<b.first;

}







signed main(){cin.tie(0);cout.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(15);

    int n,m;

    cin>>n>>m;

    VVi a(100010);

    REP(i,0,n){

        int t1,t2;

        cin>>t1>>t2;

        a[t1].pb(t2);

    }

    priority_queue<int> pq;



    int ans=0;

    REP(i,0,m+1){

        for(auto x : a[i]){

            pq.push(x);

        }

        if(!pq.empty()){

            ans+=pq.top();

            pq.pop();

        }

    }

    cout<<ans<<endl;

    return 0;

}

// Fastest known solution for this problem: