import java.util.*;
import java.io.*;

public class Main {
    static int N;
    static int M;
    
    public static void main(String[] args) {
        N = sc.nextInt();
        M = sc.nextInt();
        NavigableSet<Integer> vacancy = new TreeSet<Integer>();
        Pair[] works = new Pair[N];
        for (int i = 0; i < M; i++) 
            vacancy.add(i);
        for (int i = 0; i < N; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            works[i] = new Pair(a,b);
        }
        Arrays.sort(works);
        long answer = 0;
        for (int i = 0; i < N; i++) {
            int delay = works[i].delay;
            int value = works[i].value;
            Integer loc = vacancy.floor(M-delay);
            if (loc != null) {
                vacancy.remove(loc);
                answer += value;
            }
        }
        writer.println(answer);
        writer.flush();
    }
    static class Pair implements Comparable<Pair> {
        public int delay;
        public int value;
        public Pair(int delay, int value) {
            this.delay = delay;
            this.value = value;
        }
        public int compareTo(Pair w) {
            if (value != w.value) {
                return w.value - value;
            } else {
                return delay - w.delay;
            }
        }
    }

    static final FastScanner sc = new FastScanner(System.in);
    static PrintWriter writer = new PrintWriter(System.out);

    static class FastScanner {
        Reader input;
 
        FastScanner() {
            this(System.in);
        }
 
        FastScanner(InputStream stream) {
            this.input = new BufferedReader(new InputStreamReader(stream));
        }
 
        int nextInt() {
            return (int) nextLong();
        }
 
        long nextLong() {
            try {
                int sign = 1;
                int b = input.read();
                while ((b < '0' || '9' < b) && b != '-' && b != '+') {
                    b = input.read();
                }
                if (b == '-') {
                    sign = -1;
                    b = input.read();
                } else if (b == '+') {
                    b = input.read();
                }
                long ret = b - '0';
                while (true) {
                    b = input.read();
                    if (b < '0' || '9' < b) return ret * sign;
                    ret *= 10;
                    ret += b - '0';
                }
            } catch (IOException e) {
                e.printStackTrace();
                return -1;
            }
        }
 
        double nextDouble() {
            try {
                double sign = 1;
                int b = input.read();
                while ((b < '0' || '9' < b) && b != '-' && b != '+') {
                    b = input.read();
                }
                if (b == '-') {
                    sign = -1;
                    b = input.read();
                } else if (b == '+') {
                    b = input.read();
                }
                double ret = b - '0';
                while (true) {
                    b = input.read();
                    if (b < '0' || '9' < b) break;
                    ret *= 10;
                    ret += b - '0';
                }
                if (b != '.') return sign * ret;
                double div = 1;
                b = input.read();
                while ('0' <= b && b <= '9') {
                    ret *= 10;
                    ret += b - '0';
                    div *= 10;
                    b = input.read();
                }
                return sign * ret / div;
            } catch (IOException e) {
                e.printStackTrace();
                return Double.NaN;
            }
        }
 
        char nextChar() {
            try {
                int b = input.read();
                while (Character.isWhitespace(b)) {
                    b = input.read();
                }
                return (char) b;
            } catch (IOException e) {
                e.printStackTrace();
                return 0;
            }
        }
 
        String nextStr() {
            try {
                StringBuilder sb = new StringBuilder();
                int b = input.read();
                while (Character.isWhitespace(b)) {
                    b = input.read();
                }
                while (b != -1 && !Character.isWhitespace(b)) {
                    sb.append((char) b);
                    b = input.read();
                }
                return sb.toString();
            } catch (IOException e) {
                e.printStackTrace();
                return "";
            }
        }
    }
    //FAST SCANNER END HERE
}


Measured memory_bytes: 36204