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: Wrong Answer)

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <math.h>
using namespace std;
using std::swap;

/*
int main() {
    int A, B;
    int ad, su, mu;
    std:cin >> A >> B;
    ad = A+B;
    su = A-B;
    mu = A*B;

    std::cout << max({ad, su, mu} )<< std::endl;

    return 0;
}
 */
/*
int main(){
    int K, X;
    std::cin >> K >> X;
    for(int i=X-K+1; i<X+K; i++){
        std::cout << i << std::endl;
    }
    return 0;
}
 */

/* ローカルでは動く
string strsort(string s);

int main(){
    long int N;
    long int tmp_match=0;
    long int match=0;
    string s;
    vector<string> strs;
    std::cin >> N;
    for(int i=0; i<N; i++) {
        std::cin >> s;
        s = strsort(s);
        strs.push_back(s);
    }
    sort(strs.begin(), strs.end());
    for(int i=1; i<N; i++){
        tmp_match=0;
        while (strs[i] == strs[i - 1] && i < N) {
            tmp_match++;
            i++;
        }
        match+=(tmp_match+1)*(tmp_match)/2;
    }
    std::cout << match << std::endl;
}

string strsort(string s){
    int N=10;
    char tmp;
    for(int i=1; i<10; i++) {
        int point = i;
        while (point != 0) {
            if (s[point] < s[point - 1]) {
                swap(s[point], s[point - 1]);
                point--;
            } else {
                break;
            }
        }
    }
    return s;

}
*/
struct work{
    int reward;
    int day;
};
int main(){
    int N, M;
    int rew_sum=0;
    int point = 0;
    work wor;
    vector<work> works;
    std::cin >> N >> M;
    for(int i=0; i<N; i++){
        std::cin >> wor.day >> wor.reward;
        works.push_back(wor);
    }

    sort(works.begin(), works.end(),
         [](const work& x, const work& y) { return x.day > y.day;});
    sort(works.begin(), works.end(),
         [](const work& x, const work& y) { return x.reward > y.reward;});

    for(int i=0; i<M+1; i++) {
        while (point < N) {
            if (works[point].day < M - i + 1) {
                rew_sum += works[point].reward;
                point++;
                break;
            } else {
                point++;
            }
        }
    }
    std::cout << rew_sum << std::endl;
    return 0;
}