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 PyPy3 (2.4.0) (judge verdict: Wrong Answer)

from operator import itemgetter
import bisect
import heapq
import sys
input = sys.stdin.readline

def main():
    N,M = [int(x) for x in input().split()]
    work = {}
    for _ in range(N):
        a,b = [int(x) for x in input().split()]
        if(a in work):
            work[a].append(-b)
        else:
            work[a] = [-b]

    cand = []
    heapq.heapify(cand)
    cnt = 0
    for i in range(1,M+1):
        if(i in work):
            cand += work[i]
        if(len(cand)==0):
            continue
        x = -heapq.heappop(cand)
        cnt += x

    print(cnt)

if __name__ == '__main__':
    main()