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: Time Limit Exceeded)

import math
from functools import reduce
from collections import deque
import sys
sys.setrecursionlimit(10**7)

def s(generator, splitter, mapper):
    return [ mapper(s) for s in generator().split(splitter) ]

# スペース区切りの入力を読み込んで数値リストにして返します。
def get_nums_l():
    return [ int(s) for s in input().split(" ")]

# 改行区切りの入力をn行読み込んで数値リストにして返します。
def get_nums_n(n):
    return [ int(input()) for _ in range(n)]

n,m = get_nums_l()
jobs = list(map(lambda s:list(map(int,s.split(" "))), sys.stdin.readlines()))

jobs.sort(key=lambda job: job[0])
jobs.sort(key=lambda job: job[1], reverse=True)


mark = [True] * (m+1)
ans = 0
for job in jobs:
    nouki = job[0]
    if nouki <= m:
        while (not mark[nouki]) and (nouki < m):
            nouki += 1
        if nouki > m:
            continue
        if mark[nouki]:
            ans += job[1]
            mark[nouki] = False
        # elif mark[m]:
            # # にぶたん
            # # left 既知の右端False
            # left = nouki
            # # right 既知の左端True
            # right = m
            # while(left < right-1):
            #     center = (left+right)//2
            #     if(mark[center]):
            #         right = center
            #     else:
            #         left = center
            # ans += job[1]
            # mark[right] = False

print(ans)