// Slower C++ solution:
#include<iostream>

#include<vector>

#include<queue>



using namespace std;



vector<int>ve[120000];



int main(){

//	ios::sync_with_stdio(false);

//	cin.tie(0);cout.tie(0);

	int n,k;

	cin>>n>>k;

	int x,y;

	for(int i=0;i<n;i++){

		cin>>x>>y;

		if(x>k) continue;

		int tt=k-x+1;

		ve[tt].push_back(y);

	}

	

	priority_queue<int>q;

	int ans=0;

	for(int i=k;i>=1;i--){

		for(int j=0;j<ve[i].size();j++) q.push(ve[i][j]);

		if(!q.empty()){

			ans+=q.top();

			q.pop();	

		}

	}

	cout<<ans<<"\n";

	

	return 0;

} 

// Faster C++ solution for the same problem (measured speedup: 1.1329654146518666x):
#include<bits/stdc++.h>

#include<ext/pb_ds/assoc_container.hpp>

#include<ext/pb_ds/tree_policy.hpp>



using namespace std;

using namespace __gnu_pbds;



/* msi1427 */



#define ll           long long

#define ull          long long unsigned

#define LD           long double

#define FOR(i,n)     for(int i=0;i<n;i++)

#define FLR(i,n)     for(ll i=0;i<n;i++)

#define RFOR(i,n)    for(int i=n-1;i>=0;i--)

#define RFLR(i,n)    for(ll i=n-1;i>=0;i--)

#define rep(i,a,b)   for(int i=a;i<=b;i++)

#define repl(i,a,b)  for(ll i=a;i<=b;i++)

#define casep(z)     cout << "Case " << z << ": ";

#define Fast         ios_base::sync_with_stdio(0);cin.tie(0);

#define sz(a)        a.size()

#define all(x)       x.begin(),x.end()

#define SORT(a,n)    sort(a,a+n)

#define RSORT(a,n)   sort(a,a+n,greater<ll>())

#define pii          pair<int,int>

#define pll          pair<ll,ll>

#define tll          tuple<ll,ll,ll>

#define VSORT(v)     sort(all(v))

#define VRSORT(v)    sort(v.rbegin(),v.rend())

#define pb           push_back

#define eb           emplace_back

#define pf           push_front

#define pob          pop_back()

#define pof          pop_front()

#define ff           first

#define ss           second

#define tt           true

#define fs           false

#define MP           make_pair

#define MEM(x,n)     memset((x),n,sizeof(x))

#define bsrch(a,n,x) binary_search(a,a+n,x)

#define vi           vector<int>

#define vll          vector<ll>

#define PI           acos(-1.0)

#define LB(a,x)      (lower_bound(all(a),x)-a.begin()) //  first element in the range [first,last) which does not compare less than val.

#define UB(a,x)      (upper_bound(all(a),x)-a.begin()) //  first element in the range [first,last) which compares greater than val.

#define PQ           priority_queue

#define heap         PQ< ll , vector<ll> , greater < ll > >

#define REV(x)       reverse(all(x))

#define mpii         map<int,int>

#define mpll         map<ll,ll>

#define cig          cin.ignore()

#define INF          (ll)1e18

#define EPS          1e-9

#define prec(n)      fixed << setprecision(n)

#define lb           lower_bound

#define ub           upper_bound

#define fin          freopen("in.txt","r",stdin)

#define fout         freopen("out.txt","w",stdout)

#define sc           scanf

#define pt           printf

#define np           next_permutation

#define IT(it,x)     for(auto it=x.begin();it!=x.end();it++)

#define sci(x)       scanf("%d",&x);

#define scl(x)       scanf("%lld",&x);

#define scd(x)       scanf("%lf",&x);

#define scs(x)       scanf("%s",x);



#define min3(a,b,c)     min(a,min(b,c))

#define max3(a,b,c)     max(a,max(b,c))

#define min4(a,b,c,d)   min(min(a,b),min(c,d))

#define max4(a,b,c,d)   max(max(a,b),max(c,d))

#define max5(a,b,c,d,e) max(max3(a,b,c),max(d,e))

#define min5(a,b,c,d,e) min(min3(a,b,c),min(d,e))

#define EulerGamma      0.57721566490153286060651209



typedef

tree<

  ll,

  null_type,

  less<ll>,

  rb_tree_tag,

  tree_order_statistics_node_update>

ordered_set;



ll dx[] = {1,-1,0,0};

ll dy[] = {0,0,1,-1};



ll ceiling(ll x,ll y)

{

    if(x%y) return ((x/y)+1);

    else return (x/y);

}



ll gcd(ll x,ll y)

{

    return ((y==0)?x:gcd(y,x%y));

}



ll lcm(ll x,ll y)

{

    return ((x*y)/gcd(x,y));

}



ll BMod(ll B,ll P,ll M)

{

    ll R=1;

    B=B%M;

    while(P)

    {

        if(P&1)

            R=(R*B)%M;

        P >>= 1;

        B=(B*B)%M;

    }

    return R;

}



bool check(ll n,ll pos) {return (n&(1<<pos));}

ll SET(ll n,ll pos){return (n|(1<<pos));}

ll RESET(ll n,ll pos) {return(n&~(1<<pos));}

mt19937 rng32(chrono::steady_clock::now().time_since_epoch().count());



#define MOD 1000000007

#define MAX 100005



ll n,m,a,b;

vector<ll>v[MAX];



int main()

{

    Fast

    cin>>n>>m;

    FLR(i,n){

        cin>>a>>b;

        v[a].pb(b);

    }

    priority_queue<ll>pq;

    ll ans = 0;

    repl(i,1,m){

        FLR(r,sz(v[i])) pq.push(v[i][r]);

        if(!pq.empty()){

            ans+=pq.top();

            pq.pop();

        }

    }

    cout << ans << "\n";

}

/*



*/