Problem:
Score : 400 points

Problem Statement

There are N one-off jobs available. If you take the i-th job and complete it, you will earn the reward of B_i after A_i days from the day you do it.

You can take and complete at most one of these jobs in a day.

However, you cannot retake a job that you have already done.

Find the maximum total reward that you can earn no later than M days from today.

You can already start working today.

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq A_i \leq 10^5

1 \leq B_i \leq 10^4

Input

Input is given from Standard Input in the following format:

N M
A_1 B_1
A_2 B_2
\vdots
A_N B_N

Output

Print the maximum total reward that you can earn no later than M days from today.

Sample Input 1

3 4
4 3
4 1
2 2

Sample Output 1

5

You can earn the total reward of 5 by taking the jobs as follows:

Take and complete the first job today. You will earn the reward of 3 after four days from today.

Take and complete the third job tomorrow. You will earn the reward of 2 after two days from tomorrow, that is, after three days from today.

Sample Input 2

5 3
1 2
1 3
1 4
2 1
2 3

Sample Output 2

10

Sample Input 3

1 1
2 1

Sample Output 3

0

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>

using namespace std;

int main() {
    int N, M;
    cin >> N >> M;

    pair<int, int> p[N];
    for (int i = 0; i < N; i++) {
        cin >> p[i].first >> p[i].second;
    }

    sort(p, p + N, [](pair<int, int> x, pair<int, int> y) {
        return x.first < y.first;
    });

    priority_queue<int> pq;
    long long res = 0;
    int j = 0;
    for (int i = 1; i <= M; i++) {
        while (j < N && p[j].first <= i) {
            pq.push(p[j].second);
            j++;
        }
        if (!pq.empty()) {
            res += pq.top();
            pq.pop();
        }
    }

    cout << res << "\n";
}