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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<stdlib.h>

#define NEW(p,n){p=malloc((n)*sizeof(p[0]));if(p==NULL){printf("not enough memory\n");exit(1);};}
//pの型の変数n個の要素分のメモリを確保し、そのアドレスをpに代入するマクロ

#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define MIN(a, b) ((a) < (b) ? (a) : (b))

typedef struct{
    long price;
    int date;
}parttime;

int comp(const void* a, const void* b){
    parttime p = *(parttime *)a;
    parttime q = *(parttime *)b;
    if(p.date < q.date) return -1;
    else if(p.date > q.date) return 1;
    else{
        if(p.price < q.price) return 1;
        else if(p.price > q.price) return -1;
        else return 0;
    }
}

int main(void){
    int N,M;
    scanf("%d %d",&N, &M);

    //J[0]~J[N-1]に格納する
    parttime* J;
    NEW(J,N);
    for(int i=0;i<N;i++){
        scanf("%d %ld",&J[i].date, &J[i].price);
    }
    //dateの昇順→priceの降順にJをソート
    qsort(J,N,sizeof(J[0]),comp);

    long ans=0;
    int day=1;
    int i=0;
    while(i<N && day<=M){
        if(J[i].date <= day){
            ans+=J[i].price;
            day++;
        }
        i++;
    }

    printf("%ld\n",ans);

    return 0;
}

//dateの降順にするのも忘れないで
//123while文の中を||→&&にしたらREは出なくなった、だがWA
//サンプルケースは全部ACなのに