
Score : 400 points
Problem StatementThere 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
InputInput is given from Standard Input in the following format:
N M
A_1 B_1
A_2 B_2
\vdots
A_N B_N
OutputPrint the maximum total reward that you can earn no later than M days from today.
Sample Input 13 4
4 3
4 1
2 2
Sample Output 15
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 25 3
1 2
1 3
1 4
2 1
2 3
Sample Output 210
Sample Input 31 1
2 1
Sample Output 30
