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 Rust (1.15.1) (judge verdict: Runtime Error)

fn main() {
    let (n,m) = {let v:Vec<usize> = read_vec(); (v[0],v[1])};
    let mut ab: Vec<Vec<i32>> = read_vec2(n as u32);
    ab.sort_by(|a,b| (a[1]).partial_cmp(&b[1]).unwrap().reverse());
    let mut v:Vec<i32> = vec![0;m as usize];
    let mut end:usize = m;
    for a in ab.iter() {
        let mut t = (a[0]-1) as usize;
        while t<end && v[t]!=0  {
            t += 1;
        }
        if t < end {
            v[t] = a[1];
        } else {
            end = (a[0]-1) as usize;
        }
    }
    let ans:i32 = v.iter().sum();
    println!("{}", ans);
}

fn get_line() -> String {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).ok();
    buf.trim().to_owned()
}

fn read<T: std::str::FromStr>() -> T{
    get_line().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T>{
    get_line().split_whitespace()
        .map(|e| e.parse().ok().unwrap()).collect()
}

fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    let mut v2:Vec<Vec<T>> = Vec::new();
    for _ in 0..n {
        let mut s = String::new();
        std::io::stdin().read_line(&mut s).ok();
        let v: Vec<T> = s.trim().split_whitespace()
            .map(|e| e.parse().ok().unwrap()).collect();
        v2.push(v);
    }
    v2
}