### BUGGY CODE ###

#Binary Indexed Tree (1-index！！！！！！！！)
class BinaryIndexedTree():
    def __init__(self, size):
        self.__node = [0] * (size+1)
        self.size = size

    #node[index]にvalueを足して、BITを更新 O(logN)
    def add(self, index, value):
        while index <= self.size:
            self.__node[index] += value
            index += index&-index    
    
    #indexまでの和を返す O(logN)
    def sum(self, index):
        ret = 0 #零元・単位元
        while index > 0:
            ret += self.__node[index]
            index -= index&-index    
        return ret

    def update_max(self, index, value):
        while index <= self.size:
            self.__node[index] = max(self.__node[index], value)
            index += index & -index


    #indexまでの最大値を返す
    def query_max(self, index):
        ret = 0
        while index > 0:
            ret = max(ret, self.__node[index])
            index -= index & -index
        return ret
        
        

    #0-indexでの添字を受け取って、1-indexでの添字での値を返す
    def get_node(self, index):
        return self.__node[index]

    def show(self):
        #print(self.__node)
        for day in range(1,self.size+1):
            print("day,",day,self.sum(day))

#
# 　　  ⋀_⋀　 
#　　  (･ω･)  
# .／ Ｕ ∽ Ｕ＼
#  │＊　合　＊│
#  │＊　格　＊│ 
#  │＊　祈　＊│ 
#  │＊　願　＊│ 
#  │＊　　　＊│ 
#      ￣
#
import sys
sys.setrecursionlimit(10**6)
input=sys.stdin.readline
from math import floor,ceil,sqrt,factorial,log #log2ないｙｐ
from heapq import heappop, heappush, heappushpop
from collections import Counter,defaultdict
from itertools import accumulate,permutations,combinations,product,combinations_with_replacement
from bisect import bisect_left,bisect_right
from copy import deepcopy
from operator import itemgetter
inf=float('inf')
mod = 10**9+7
def INT_(n): return int(n)-1
def MI(): return map(int,input().split())
def MF(): return map(float, input().split())
def MI_(): return map(INT_,input().split())
def LI(): return list(MI())
def LI_(): return [int(x) - 1 for x in input().split()]
def LF(): return list(MF())
def LIN(n:int): return [I() for _ in range(n)]
def LLIN(n: int): return [LI() for _ in range(n)]
def LLIN_(n: int): return [LI_() for _ in range(n)]
def LLI(): return [list(map(int, l.split() )) for l in input()]
def I(): return int(input())
def F(): return float(input())
def ST(): return input().replace('\n', '')
def main():
    N,M= MI()
    works = LLIN(N)
    works.sort(key = itemgetter(1),reverse = True)
    BIT = BinaryIndexedTree(M)
    used = set()
    #print(works)

    for day in range(1,M+1):
        #print(day)
        BIT.add(day,1)
    ans = 0
    for day, money in works:
        #BIT.show()
        date = M-day+1
        while date in used:
            date-=1
        if date > 0 and BIT.sum(date)>0:
            BIT.add(date, -1)
            used.add(date)
            ans += money

    print(ans)
    
    
if __name__ == '__main__':
    main()

### FIXED CODE ###


import sys
sys.setrecursionlimit(10**6)
input=sys.stdin.readline
from math import floor,ceil,sqrt,factorial,log #log2ないｙｐ
from heapq import heappop, heappush, heappushpop
from collections import Counter,defaultdict
from itertools import accumulate,permutations,combinations,product,combinations_with_replacement
from bisect import bisect_left,bisect_right
from copy import deepcopy
from operator import itemgetter
inf=float('inf')
mod = 10**9+7
def INT_(n): return int(n)-1
def MI(): return map(int,input().split())
def MF(): return map(float, input().split())
def MI_(): return map(INT_,input().split())
def LI(): return list(MI())
def LI_(): return [int(x) - 1 for x in input().split()]
def LF(): return list(MF())
def LIN(n:int): return [I() for _ in range(n)]
def LLIN(n: int): return [LI() for _ in range(n)]
def LLIN_(n: int): return [LI_() for _ in range(n)]
def LLI(): return [list(map(int, l.split() )) for l in input()]
def I(): return int(input())
def F(): return float(input())
def ST(): return input().replace('\n', '')
def main():
    N,M= MI()
    works = []
    for _ in range(N):
        date,money = map(int,input().split())
        works.append((-money,date))
    works.sort(key = itemgetter(1),reverse = True)

    ans =0

    pri_queue = []
    for date in range(M):
        while works and works[-1][1] -1 <= date:
            heappush(pri_queue,works.pop())
        if pri_queue:
            ans += -heappop(pri_queue)[0]

    print(ans)
    
    
if __name__ == '__main__':
    main()