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 Python (3.4.3) (judge verdict: Time Limit Exceeded)

#coding: utf-8
from operator import itemgetter

args = input().split()

# バイトの件数
N = int(args[0])
# ゴールの日
M = int(args[1])

work_list = {}
for i in range(N):
    work = input().split()
    key = int(work[0])
    value = int(work[1])
    if key in work_list:
        pass
    else:
        work_list[key] = []

    work_list[key].append(value)

current = M
money = 0
while current >= 0:
    lst = []
    for key in work_list.keys():
        if current + key <= M:
            work_list[key] = sorted(work_list[key])
            work_list[key].reverse()
            lst.append([work_list[key][0], key])

    lst = sorted(lst)
    lst.reverse()
    if len(lst) > 0:
        money += lst[0][0]
        del(work_list[lst[0][1]][0])
        if len(work_list[lst[0][1]]) == 0:
            del(work_list[lst[0][1]])
    current -= 1

print(money)