import java.io.*;
import java.util.*;
import static java.lang.System.out;

public class Main {
    static MyReader in = new MyReader();

    public static void main(String[] args) {
        int N = in.i();
        int M = in.i();
        MyQueue q1 = new MyQueue(N);
        for (int i = 0; i < N; i++) {
            int a = in.i();
            int b = in.i();
            q1.push(new int[]{a, b});
        }
        q1.sort();
        PriorityQueue<Integer> q2 = new PriorityQueue<>((x, y) -> -x + y);
        long ans = 0;
        for (int i = 1; i <= M; i++) {
            while (!q1.isEmpty() && q1.peek()[0] == i) {
                q2.add(q1.pop()[1]);
            }
            if (!q2.isEmpty()) {
                ans += q2.poll();
            }
        }

        out.println(ans);
    }
}

class MyQueue {
    final int MAX;
    int[][] array;
    int head = 0;
    int tail = 0;
    int count = 0;

    MyQueue(int N) {
        MAX = N;
        array = new int[N][];
    }

    void push(int[] a) {
        array[tail] = a;
        if (++tail == MAX) tail = 0;
        count++;
    }

     int[] pop() {
        int[] a = array[head];
        if (++head == MAX) head = 0;
        count--;
        return a;
    }

    int[] peek() {
        return array[head];
    }

    boolean isEmpty() {
        return count == 0;
    }

    void sort() {
        Arrays.sort(array, (x, y) -> x[0] - y[0]);
    }
}

class MyReader extends BufferedReader {
    char[] cbuf = new char[1024];
    int head = 0;
    int tail = 0;

    MyReader() {
        super(new InputStreamReader(System.in));
    }

    char next() {
        if (head == tail) {
            try {
                tail = super.read(cbuf, 0, cbuf.length);
            } catch (IOException e) {
                e.printStackTrace();
            }
            head = 0;
        }
        return cbuf[head++];
    }

    void back() {
        head--;
    }

    boolean minus() {
        boolean minus;
        while (true) {
            char c = next();
            if (!isDelimiter(c)) {
                if (!(minus = c == '-')) back();
                return minus;
            }
        }
    }

    void skip() {
        while (isDelimiter(next()));
        back();
    }

    char[] s(int N) {
        char[] cbuf = new char[N];
        read(cbuf, 0, N);
        return cbuf;
    }

    public int read(char[] cbuf, int off, int len) {
        skip();
        int i;
        for (i = 0; i < cbuf.length; i++) {
            char c = next();
            if (isDelimiter(c)) {
                break;
            }
            cbuf[i] = c;
        }
        return i;
    }

    boolean isDelimiter(char c) {
        return c == ' ' || c == '\n' || c == '\r';
    }

    int i() {
        boolean minus = minus();
        int n = 0;
        while (true) {
            int k = next() - '0';
            if (k < 0 || 9 < k) break;
            n = 10 * n + k;
        }
        return minus ? -n : n;
    }

    int[] ii(final int N) {
        int[] a = new int[N];
        for (int j = 0; j < a.length; j++) a[j] = i();
        return a;
    }

    long l() {
        boolean minus = minus();
        long n = 0;
        while (true) {
            int k = next() - '0';
            if (k < 0 || 9 < k) break;
            n = 10 * n + k;
        }
        return minus ? -n : n;
    }
}


Measured memory_bytes: 43636