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: Wrong Answer)

def main():
    [N, M] = [int(number) for number in input().split()]
    part_times = []
    for i in range(N):
        [a, b] = [int(number) for number in input().split()]
        #money_par_day = b / a
        part_times.append([b, a])
        #part_times.sort(reverse=True)
    part_times = sorted(part_times, key = lambda x: (x[0], x[1]), reverse=True)
    money = 0
    day = 0

    #while day <= M:

    for part_time in part_times:
        [b,a] = part_time
        if a + day <= M:
            day += 1
            money += b
        else:
            continue
    print(money)

if __name__ == '__main__':
    main()