Problem:
Score : 400 points

Problem Statement

There are N one-off jobs available. If you take the i-th job and complete it, you will earn the reward of B_i after A_i days from the day you do it.

You can take and complete at most one of these jobs in a day.

However, you cannot retake a job that you have already done.

Find the maximum total reward that you can earn no later than M days from today.

You can already start working today.

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq A_i \leq 10^5

1 \leq B_i \leq 10^4

Input

Input is given from Standard Input in the following format:

N M
A_1 B_1
A_2 B_2
\vdots
A_N B_N

Output

Print the maximum total reward that you can earn no later than M days from today.

Sample Input 1

3 4
4 3
4 1
2 2

Sample Output 1

5

You can earn the total reward of 5 by taking the jobs as follows:

Take and complete the first job today. You will earn the reward of 3 after four days from today.

Take and complete the third job tomorrow. You will earn the reward of 2 after two days from tomorrow, that is, after three days from today.

Sample Input 2

5 3
1 2
1 3
1 4
2 1
2 3

Sample Output 2

10

Sample Input 3

1 1
2 1

Sample Output 3

0

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <cstddef>
#include <cstdint>
#include <vector>

namespace null_null {

using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using usize = std::size_t;

constexpr usize operator"" _z(unsigned long long x) noexcept {
  return static_cast<usize>(x);
}

template <typename T>
std::vector<T> make_v(usize a) { return std::vector<T>(a); }
template <typename T, typename... Ts>
auto make_v(usize a, Ts... ts) {
  return std::vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template <typename T, typename V>
typename std::enable_if<std::is_class<T>::value == 0>::type
fill_v(T &t, const V &v) { t = v; }
template <typename T, typename V>
typename std ::enable_if<std::is_class<T>::value != 0>::type
fill_v(T &t, const V &v) {
  for (auto &e : t) fill_v(e, v);
}

template <typename T, typename V>
inline void chmin(T &a, V b) {
  if (a > b) a = b;
}
template <typename T, typename V>
inline void chmax(T &a, V b) {
  if (a < b) a = b;
}

} // namespace null_null

#include <algorithm>
#include <iostream>
#include <set>
#include <utility>

namespace null_null {

void main_() {
  i32 N, M;
  std::cin >> N >> M;
  std::vector<std::pair<i32, i32>> v(N);
  for (usize i = 0; i < N; i++) std::cin >> v[i].second >> v[i].first;
  std::sort(v.begin(), v.end());
  std::reverse(v.begin(), v.end());
  std::set<i32> s;

  for (i32 i = -M; i <= 0; i++) s.insert(i);
  s.insert(10);
  i32 ans = 0;

  for (auto x : v) {
    i32 day = *(s.lower_bound(x.second - M));
    if (day == 10) {
      continue;
    } else {
      s.erase(day);
      ans += x.first;
    }
  }

  std::cout << ans << std::endl;
}

} // namespace null_null

int main() {
  null_null::main_();
  return 0;
}