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 ####
import sys
import math
from collections import defaultdict

#### 設定 ####
sys.setrecursionlimit(10**7)

#### 定数 ####
mod = 10**9 + 7

#### 読み込み ####
def I(): return int(input())
def II(): return map(int, input().split())
def III(): return list(map(int, input().split()))
def Line(N):
  read_all = [tuple(map(int, input().split())) for _ in range(N)]
  return map(list,zip(*read_all))

#################

N,M = II()
A,B = Line(N)
a = []
for i in range(N):
  a.append([A[i],B[i]])
a.sort(key = lambda x:(-x[1]))

from bisect import bisect_left
s = [i for i in range(1,M+1)]
ans = 0
for i in range(N):
  if a[i][0]<=M:
    place = bisect_left(s,a[i][0])
    if place <= len(s)-1:
      s.pop(place)
      ans += a[i][1]
print(ans)