#include <bits/stdc++.h>
using namespace std;

#define int long long
#define itn int
#define For(i, a, b) for (int i = (a); i <= static_cast<int>(b); i++)
#define Forr(i, a, b) for (int i = (a); i >= static_cast<int>(b); i--)
#define rep(i, n) For(i, 0, n - 1)
#define repall(i, arr) for (auto& i : (arr))
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define dump(x) cerr << #x << " = " << (x) << '\n'
#define dump2(x, y) \
    cerr << #x << " = " << (x) << " " << #y << " = " << (y) << '\n'
#define SZ(x) ((int)(x).size())
#define bit(n) (1LL << (n))
constexpr int MOD = 1e9 + 7;

template <typename T>
using pq = priority_queue<T>;
template <typename T>
using pqr = priority_queue<T, vector<T>, greater<T>>;
const int INF = LLONG_MAX / 2;
using P = pair<int, int>;
using vec = vector<int>;
template <typename T>
using mat = vector<vector<T>>;

template <typename T1, typename T2>
ostream& operator<<(ostream& stream, const pair<T1, T2>& p) {
    return stream << p.first << " " << p.second;
}
template <typename T>
void print(const vector<T> vec) {
    unsigned int len = vec.size();
    rep (i, len - 1)
        cout << vec[i] << ' ';
    cout << vec[len - 1] << '\n';
}
template <typename Arg>
void print(const Arg arg) {
    cout << arg << '\n';
}
template <typename Head, typename... Args>
void print(const Head head, const Args... args) {
    cout << head << " ";
    print(args...);
}
template <typename T>
T sum_(vector<T> vec, T init = 0) {
    return std::accumulate(all(vec), T(init));
}

template <typename T>
void init(vector<T>& v) {
    rep (i, v.size())
        cin >> v[i];
}

template <typename T, typename U>
void init(vector<T>& v, vector<U>& w) {
    assert(v.size() == w.size());
    rep (i, v.size())
        cin >> v[i] >> w[i];
}

// clang-format off
template<typename T>
bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }
template<typename T>
bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }
template <typename T>
int index(const T& vec, const typename T::iterator it) { return distance(vec.begin(), it); }
template <typename T = int>
mat<T> mmat(int n, int m) { return mat<T>(n, vector<T>(m)); }
template <typename T = int>
vector<T> ivec(int n) { vector<T> v(n); init(v); return v; }
// clang-format on

void yn(bool tf) { print(tf ? "Yes" : "No"); }
void YN(bool tf) { print(tf ? "YES" : "NO"); }

int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }

// -------------------------------------------------------------------
// sort 1 2 3 4
// pqr 1 2 3 must impl >

signed main() {
    cin.tie(0), cout.tie(0), ios::sync_with_stdio(false);
    int n, m;
    cin >> n >> m;
    vector<P> v;
    pq<int> q;
    int a, b;
    rep (i, n) {
        cin >> a >> b;
        v.pb({a, b});
    }
    sort(all(v));

    int idx = 0;
    int ans = 0;
    For(i, 1, m) {
        if (idx < n) {
            while (v[idx].first <= i) {
                if (idx >= n) break;
                q.push(v[idx].second);
                idx++;
            }
        }
        if (!q.empty()) {
            ans += q.top();
            q.pop();
        }
    }
    print(ans);

    return 0;
}


Measured memory_bytes: 3568