#!/usr/bin/env python3
from heapq import*
(N, M), *t = [map(int, s.split()) for s in open(0)]
q = [0] * 10**5
v = [[] for _ in q]
for a, b in t:
    v[a - 1] += b,
z = 0
for i in v[:M]:
    for j in i:
        heappush(q, -j)
    z += -heappop(q)
print(z)