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.

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.

Constraints

• All values in input are integers.
• $1 \leq N \leq 10^5$
• $1 \leq M \leq 10^5$
• $1 \leq A_i \leq 10^5$
• $1 \leq B_i \leq 10^4$

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

见题面 Input 部分

见题面 Output 部分