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: Time Limit Exceeded)

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

typedef struct{
	int delay;
    int pay;
} dualint;

int comp(const void *a, const void *b)
{
	int i;
	i = - ((dualint*)a)->pay + ((dualint*)b)->pay;
	if (i)return i;
	else return  ((dualint*)a)->delay - ((dualint*)b)->delay;
}

int main()
{
	int i, j, n, m;
	int income = 0;
	dualint d[100000];
	scanf("%d%d", &n, &m);
	for (i = 0; i < n; i++) {
		scanf("%d%d", &d[i].delay, &d[i].pay);
	}
	qsort(d, n, sizeof(dualint), comp);
	int day = m - 1;
	int flag = 0;
	while (day >= 0) {
		i = 0;
		flag = 0;
		while (!flag && i < n) {
			if (d[i].delay <= m - day) {
				income += d[i].pay;
				d[i].delay = 999999;
				flag = 1;
			}
			else {
				i++;
			}
		}
		day--;
	}
	printf("%d\n", income);
	return 0;
}