#pragma GCC optimize ("O3")
#include "bits/stdc++.h"

using namespace std;
using ll = long long int;

#define debugos cout
#define debug(v) {printf("L%d %s > ",__LINE__,#v);debugos<<(v)<<endl;}
#define debugv(v) {printf("L%d %s > ",__LINE__,#v);for(auto e:(v)){debugos<<e<<" ";}debugos<<endl;}
#define debuga(m,w) {printf("L%d %s > ",__LINE__,#m);for(int x=0;x<(w);x++){debugos<<(m)[x]<<" ";}debugos<<endl;}
#define debugaa(m,h,w) {printf("L%d %s >\n",__LINE__,#m);for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){debugos<<(m)[y][x]<<" ";}debugos<<endl;}}
#define all(v) (v).begin(),(v).end()
#define repeat(cnt,l) for(auto cnt=decltype(l)();(cnt)<(l);++(cnt))
#define rrepeat(cnt,l) for(auto cnt=(l)-1;0<=(cnt);--(cnt))
#define iterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);++(cnt))
#define diterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);--(cnt))
const ll MD = 1000000007ll; const long double PI = 3.1415926535897932384626433832795L;
inline void assert_call(bool assertion, function<void()> f) { if (!assertion) { cerr << "assertion fault:" << endl; f(); abort(); } }
template<typename T1, typename T2> inline ostream& operator <<(ostream &o, const pair<T1, T2> p) { o << '(' << p.first << ':' << p.second << ')'; return o; }
template<typename Vec> inline ostream& _ostream_vecprint(ostream& os, const Vec& a) {
    os << '['; for (const auto& e : a) os << ' ' << e << ' '; os << ']'; return os; }
template<typename T> inline ostream& operator<<(ostream& o, const vector<T>& v) { return _ostream_vecprint(o, v); }
template<typename T, size_t S> inline ostream& operator<<(ostream& o, const array<T, S>& v) { return _ostream_vecprint(o, v); }
template<typename T> inline T& chmax(T& to, const T& val) { return to = max(to, val); }
template<typename T> inline T& chmin(T& to, const T& val) { return to = min(to, val); }
void bye(string s, int code = 0) { cout << s << endl; exit(code); }
mt19937_64 randdev(8901016);
template<typename T, typename Random = decltype(randdev), typename enable_if<is_integral<T>::value>::type* = nullptr>
inline T rand(T l, T h, Random& rand = randdev) { return uniform_int_distribution<T>(l, h)(rand); }
template<typename T, typename Random = decltype(randdev), typename enable_if<is_floating_point<T>::value>::type* = nullptr>
inline T rand(T l, T h, Random& rand = randdev) { return uniform_real_distribution<T>(l, h)(rand); }

#if defined(_WIN32) || defined(_WIN64)
#define getc_x _getc_nolock
#define putc_x _putc_nolock
#elif defined(__GNUC__)
#define getc_x getc_unlocked
#define putc_x putc_unlocked
#else
#define getc_x getc
#define putc_x putc
#endif
#define isvisiblechar(c) (0x21<=(c)&&(c)<=0x7E)
class MaiScanner {
    FILE* fp_;
public:
    inline MaiScanner(FILE* fp):fp_(fp){}
    template<typename T> void input_integer(T& var) noexcept {
        var = 0; T sign = 1;
        int cc = getc_x(fp_);
        for (; cc < '0' || '9' < cc; cc = getc_x(fp_))
            if (cc == '-') sign = -1;
        for (; '0' <= cc && cc <= '9'; cc = getc_x(fp_))
            var = (var << 3) + (var << 1) + cc - '0';
        var = var * sign;
    }
    inline int c() noexcept { return getc_x(fp_); }
    inline MaiScanner& operator>>(int& var) noexcept { input_integer<int>(var); return *this; }
    inline MaiScanner& operator>>(long long& var) noexcept { input_integer<long long>(var); return *this; }
    inline MaiScanner& operator>>(string& var) {
        int cc = getc_x(fp_);
        for (; !isvisiblechar(cc); cc = getc_x(fp_));
        for (; isvisiblechar(cc); cc = getc_x(fp_))
            var.push_back(cc);
        return *this;
    }
    template<typename IT> inline void in(IT begin, IT end) { for (auto it = begin; it != end; ++it) *this >> *it; }
};
class MaiPrinter {
    FILE* fp_;
public:
    inline MaiPrinter(FILE* fp):fp_(fp){}
    template<typename T>
    void output_integer(T var) noexcept {
        if (var == 0) { putc_x('0', fp_); return; }
        if (var < 0)
            putc_x('-', fp_),
            var = -var;
        char stack[32]; int stack_p = 0;
        while (var)
            stack[stack_p++] = '0' + (var % 10),
            var /= 10;
        while (stack_p)
            putc_x(stack[--stack_p], fp_);
    }
    inline MaiPrinter& operator<<(char c) noexcept { putc_x(c, fp_); return *this; }
    inline MaiPrinter& operator<<(int var) noexcept { output_integer<int>(var); return *this; }
    inline MaiPrinter& operator<<(long long var) noexcept { output_integer<long long>(var); return *this; }
    inline MaiPrinter& operator<<(char* str_p) noexcept { while (*str_p) putc_x(*(str_p++), fp_); return *this; }
    inline MaiPrinter& operator<<(const string& str) {
        const char* p = str.c_str();
        const char* l = p + str.size();
        while (p < l) putc_x(*p++, fp_);
        return *this;
    }
    template<typename IT> void join(IT begin, IT end, char sep = ' ') { for (bool b = 0; begin != end; ++begin, b = 1) b ? *this << sep << *begin : *this << *begin; }
};
MaiScanner scanner(stdin);
MaiPrinter printer(stdout);



// 

int N, M;
vector<int> T[100010];
vector<int> U[100010];

int sche[200010];

//

int main() {
    scanner >> N >> M;
    
    repeat(i, N) {
        int a, b;
        scanner >> a >> b;
        T[a].push_back(b);
    }
    repeat(i, M+5) { 
        sort(all(T[i]), greater<int>());
        // repeat(j, int(T[i].size())) chmax(sche[i+j], T[i][j]);
    }
    ll ans = 0;
    // int rem = M;
    // repeat(i, M) {
    //     chmin(rem, M - i);
    //     while (0 <= rem && T[rem].empty()) {
    //         --rem;
    //     }
    //     if (rem < 0) break;
    //     ans += T[rem].back(); T[rem].pop_back();
    // }
    priority_queue<pair<int, pair<int, int>>> pq;
    iterate(i, 1, M+1) {
        if (!T[i].empty())
            pq.emplace(T[i].front(), pair<int,int>(i, 0));
        if (!pq.empty()) {
            auto p = pq.top(); pq.pop();
            //cout << p << endl;
            ans += p.first;
            if (p.second.second+1 < T[p.second.first].size())
                pq.emplace(T[p.second.first][p.second.second+1], pair<int,int>(p.second.first, p.second.second+1));
        }
    }
    
    cout << ans << endl;
    
    return 0;
}


Measured memory_bytes: 8064