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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;

#define pb push_back
#define ll long long
#define maxn 100005
#define fr(i,j,k) for(int i=j;i<k;i++)
#define f(n) fr(i,0,n)
#define f1(n) fr(i,1,n+1)
#define ms(i) memset(i,0,sizeof(i));
#define ms1(i) memset(i,-1,sizeof(i));
#define F first
#define S second
const ll mod =1e9+7;

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n,m;
    cin >> n >> m;
    vector<int>v[100005];
    f(n){
        int a,b;
        cin >> a >> b;
        v[a].pb(b);
    }
    multiset<int>st;
    int ans = 0;
    f1(m){
        for(auto j:v[i]){
            st.insert(j);
        }
        if(st.size()){
            ans += *(--st.end());
            st.erase(--st.end());
        }
    }
    cout << ans << endl;
}