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 Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

type task struct{ a, b int }
type tasks []task

func (t tasks) Len() int           { return len(t) }
func (t tasks) Swap(i, j int)      { t[i], t[j] = t[j], t[i] }
func (t tasks) Less(i, j int) bool { return t[i].b > t[j].a }

func main() {
	var n, m int
	fmt.Scan(&n, &m)

	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	ts := tasks(make([]task, n))
	for i := range ts {
		sc.Scan()
		ts[i].a, _ = strconv.Atoi(sc.Text())
		sc.Scan()
		ts[i].b, _ = strconv.Atoi(sc.Text())
	}

	sort.Sort(ts)
	ti := 0
	ans := 0
lb:
	for i := 0; i < m; i++ {
		for i+ts[ti].a > m {
			ti++
			if ti == len(ts) {
				break lb
			}
		}
		ans += ts[ti].b
		ti++
		if ti == len(ts) {
			break lb
		}
	}
	fmt.Println(ans)
}