### BUGGY CODE ###

mod = 10 ** 9 + 7
from collections import deque
import heapq


def main():
    N, M = iip(False)
    A = []
    for i in range(N):
        A.append(iip(True))

    ret = solve(N, M, A)
    print(ret)


def solve(N, M, A):
    A = sorted(A, key=lambda x: x[1], reverse=True)

    sch = list(range(M))

    ret = 0
    for nouki, money in A:
        day = M - nouki
        if day < 0:
            continue

        id = koenai_saidai_x_index(sch, day)
        #print(sch)
        #print(nouki, money, id)
        if id is False:
            continue
        sch.pop(id)

        ret += money

    return ret


#####################################################ライブラリ集ここから

def split_print_space(s):
    print(" ".join([str(i) for i in s]))


def split_print_enter(s):
    print("\n".join([str(i) for i in s]))

def koenai_saidai_x_index(sorted_list, n):
    l = 0
    r = len(sorted_list)
    if len(sorted_list) == 0:
        return False
    if sorted_list[0] > n:
        return False

    while r-l > 1:
        x = (l+r)//2
        if sorted_list[x] == n:
            return x
        elif sorted_list[x] > n:
            r = x
        else:
            l = x
    return l

def searchsorted(sorted_list, n, side):
    if side not in ["right", "left"]:
        raise Exception("sideはrightかleftで指定してください")

    l = 0
    r = len(sorted_list)

    if n > sorted_list[-1]:
        # print(sorted_list)
        return len(sorted_list)
    if n < sorted_list[0]:
        return 0

    while r - l > 1:
        x = (l + r) // 2
        if sorted_list[x] > n:
            r = x
        elif sorted_list[x] < n:
            l = x
        else:
            if side == "left":
                r = x
            elif side == "right":
                l = x

    if side == "left":
        if sorted_list[l] == n:
            return r - 1
        else:
            return r

    if side == "right":
        if sorted_list[l] == n:
            return l + 1
        else:
            return l


def iip(listed):
    ret = [int(i) for i in input().split()]
    if len(ret) == 1 and not listed:
        return ret[0]
    return ret


def soinsuu_bunkai(n):
    ret = []
    for i in range(2, int(n ** 0.5) + 1):
        while n % i == 0:
            n //= i
            ret.append(i)
        if i > n:
            break
    if n != 1:
        ret.append(n)
    return ret


def conbination(n, r, mod, test=False):
    if n <= 0:
        return 0
    if r == 0:
        return 1
    if r < 0:
        return 0
    if r == 1:
        return n
    ret = 1
    for i in range(n - r + 1, n + 1):
        ret *= i
        ret = ret % mod

    bunbo = 1
    for i in range(1, r + 1):
        bunbo *= i
        bunbo = bunbo % mod

    ret = (ret * inv(bunbo, mod)) % mod
    if test:
        # print(f"{n}C{r} = {ret}")
        pass
    return ret


def inv(n, mod):
    return power(n, mod - 2)


def power(n, p):
    if p == 0:
        return 1
    if p % 2 == 0:
        return (power(n, p // 2) ** 2) % mod
    if p % 2 == 1:
        return (n * power(n, p - 1)) % mod


if __name__ == "__main__":
    main()

### FIXED CODE ###

mod = 10 ** 9 + 7
from collections import deque
import heapq


def main():
    N, M = iip(False)
    A = []
    for i in range(N):
        A.append(iip(True))

    ret = solve(N, M, A)
    print(-ret)


def solve(N, M, A):
    A = deque(sorted(A, key=lambda x: x[0], reverse=False))

    jobs = []
    heapq.heapify(jobs)

    ret = 0
    for day in range(M):
        nokori = day + 1

        dn = 0
        #print(nokori)
        #print(A)
        for job in A:
            if job[0] == nokori:
                heapq.heappush(jobs, -job[1])
                dn += 1
            else:
                break
        for i in range(dn):
            A.popleft()

        #print(jobs)
        if jobs:
            #print(jobs)
            ret += heapq.heappop(jobs)

        #print(nokori)
        #print(jobs)
        #print(A)

    return ret


#####################################################ライブラリ集ここから

def split_print_space(s):
    print(" ".join([str(i) for i in s]))


def split_print_enter(s):
    print("\n".join([str(i) for i in s]))

def koenai_saidai_x_index(sorted_list, n):
    l = 0
    r = len(sorted_list)
    if len(sorted_list) == 0:
        return False
    if sorted_list[0] > n:
        return False

    while r-l > 1:
        x = (l+r)//2
        if sorted_list[x] == n:
            return x
        elif sorted_list[x] > n:
            r = x
        else:
            l = x
    return l

def searchsorted(sorted_list, n, side):
    if side not in ["right", "left"]:
        raise Exception("sideはrightかleftで指定してください")

    l = 0
    r = len(sorted_list)

    if n > sorted_list[-1]:
        # print(sorted_list)
        return len(sorted_list)
    if n < sorted_list[0]:
        return 0

    while r - l > 1:
        x = (l + r) // 2
        if sorted_list[x] > n:
            r = x
        elif sorted_list[x] < n:
            l = x
        else:
            if side == "left":
                r = x
            elif side == "right":
                l = x

    if side == "left":
        if sorted_list[l] == n:
            return r - 1
        else:
            return r

    if side == "right":
        if sorted_list[l] == n:
            return l + 1
        else:
            return l


def iip(listed):
    ret = [int(i) for i in input().split()]
    if len(ret) == 1 and not listed:
        return ret[0]
    return ret


def soinsuu_bunkai(n):
    ret = []
    for i in range(2, int(n ** 0.5) + 1):
        while n % i == 0:
            n //= i
            ret.append(i)
        if i > n:
            break
    if n != 1:
        ret.append(n)
    return ret


def conbination(n, r, mod, test=False):
    if n <= 0:
        return 0
    if r == 0:
        return 1
    if r < 0:
        return 0
    if r == 1:
        return n
    ret = 1
    for i in range(n - r + 1, n + 1):
        ret *= i
        ret = ret % mod

    bunbo = 1
    for i in range(1, r + 1):
        bunbo *= i
        bunbo = bunbo % mod

    ret = (ret * inv(bunbo, mod)) % mod
    if test:
        # print(f"{n}C{r} = {ret}")
        pass
    return ret


def inv(n, mod):
    return power(n, mod - 2)


def power(n, p):
    if p == 0:
        return 1
    if p % 2 == 0:
        return (power(n, p // 2) ** 2) % mod
    if p % 2 == 1:
        return (n * power(n, p - 1)) % mod


if __name__ == "__main__":
    main()