summer

#include<iostream>
#include<queue>
#include<algorithm>
using namespace std;

struct info{
    int a, b;

    bool operator< (const info &tmp) const {
        return b < tmp.b;
    }
};

bool cmp_a(info i1, info i2){
    return i1.a < i2.a;
}

const int N = 1e5+10;
info v[N];
int n, m;

int main(){
    cin >> n >> m;
    for(int i=0; i < n; i++){
        cin >> v[i].a >> v[i].b;
    }
    sort(v, v+n, cmp_a);
    priority_queue<info> q;
    int index = 0;
    int ans = 0;
    for(int i=0; i <= m; i++){
        while(index < n and v[index].a <= i) q.push(v[index++]);
        if(q.size()) ans += q.top().b, q.pop();
    }
    cout << ans << endl;
}