//  [cpp]
/*
    Converted from Scratch by scratch2cpp (https://github.com/yos1up/scratch2cpp).
*/
#include <iostream>
#include <stdlib.h>
#include <string>
#include <vector>
#include <algorithm>
#include <math.h>
#define debug cerr << "--" << __LINE__ << "--" << "\n"
typedef long long ll;
using namespace std;

class Var{ // NOTE: immutable
public:
    mutable string sval;
    mutable long double dval;
    enum NumericState {UNKNOWN = -1, STRINGY = 0, NUMERIC = 1};
    mutable NumericState numericState;
    mutable bool svalValid, dvalValid; // TODO: initialize at here?

    Var(){
        *this = Var("");
    }
    Var(string s){
        sval = s;
        svalValid = true; dvalValid = false;
        numericState = UNKNOWN;
    }
    Var(long double d){
        dval = d;
        svalValid = false; dvalValid = true;
        numericState = NUMERIC;
    }
    Var(const Var &v){
        sval = string(v.sval); dval = v.dval;
        svalValid = v.svalValid; dvalValid = v.dvalValid;
        numericState = v.numericState;
    }
    void fillDval() const{
        if (dvalValid) return;
        double d;
        bool numeric = isNumericString(sval, &d);
        if (numeric){
            numericState = NUMERIC;
            dval = d;
        }else{
            numericState = STRINGY;
            dval = 0.0;
        }        
        dvalValid = true;
    }
    static bool isNumericString(const string &s, double *ptr) {
        char* ep;
        // cause side-effect: errno can be ERANGE after calling strtod
        *ptr = strtod(s.c_str(), &ep);
        // TODO: support long double (with strtold)
        // Scratch 3.0 recognize the string cause underflows or overflows as Numeric
        return NULL != ep && '\0' == ep[0] && s[0] != '\0';
    }
    bool isNumeric() const{
        fillDval();
        return numericState == NUMERIC;
    }    
    void fillSval() const{
        if (svalValid) return;
        sval = (floor(dval) == dval) ? to_string((ll)dval) : to_string(dval);
        svalValid = true;
    }       
    long double asNumber() const{
        fillDval();
        return dval;
    } 
    string asString() const{
        fillSval();
        return sval;
    }
    Var operator+(const Var &y) const{
        return Var(this->asNumber() + y.asNumber());
    }
    Var operator+=(const Var &y){
        *this = *this + y;
        return *this;
    }
    Var operator-(const Var &y) const{
        return Var(this->asNumber() - y.asNumber());
    }
    Var operator*(const Var &y) const{
        return Var(this->asNumber() * y.asNumber());
    }
    Var operator/(const Var &y) const{
        return Var(this->asNumber() / y.asNumber());
    }
    Var operator%(const Var &y) const{
        return Var(fmod(this->asNumber(), y.asNumber()));
    }
    bool operator<(const Var &y) const{
        if (this->isNumeric() && y.isNumeric()){
            return this->asNumber() < y.asNumber();
        } // compare as number if both can be interpreted as numeric
        return this->asString() < y.asString();
    }
    bool operator>(const Var &y) const{
        return y < *this;
    }
    bool operator==(const Var &y) const{
        if (this->isNumeric() && y.isNumeric()){
            return this->asNumber() == y.asNumber();
        } // compare as numeric if both are numeric
        return this->asString() == y.asString();
    }
    friend ostream& operator << (ostream& os, const Var& p);
    friend istream& operator >> (istream& is, const Var& p);
};
ostream& operator << (ostream& os, const Var& p){
    os << p.asString();
    return os;
}
istream& operator >> (istream& is, Var& p){
    string s; is >> s; p = Var(s);
    return is;
}


Var letterOf(Var index, Var sourceString){
    /* index: 1-origined */
    string str = sourceString.asString();
    int idx = (int)(index.asNumber() - 1);
    // seem to be dirty but Scratch seems to do like this.
    // ex. letterOf(0.01, "world") == "w", letterOf(1.99, "world") == "w", letterOf(5.99, "world") == "d"
    if (0 <= idx && idx < str.size()) return Var(str.substr(idx, 1));
    return Var();
}

class VarList{
public:
    vector<Var> data;
    VarList(const vector<Var> &x) { data = x; }
    void push_back(const Var &x){ data.push_back(x); }
    void pop_back(){ data.pop_back(); }
    void clear(){ data.clear(); }
    int size(){ return (int) data.size(); }
    Var getLineOfList(const Var &index) const{
        /* index: 1-origined */
        int idx = (int)index.asNumber() - 1;
        // (unlike 'letterOf', index==0.9 does not work.)
        if (0 <= idx && idx < data.size()) return data[idx];
        return Var();
    }
    void setLineOfListTo(const Var &index, const Var &v){
        /* index: 1-origined */
        int idx = (int)index.asNumber() - 1;
        if (0 <= idx && idx < data.size()) data[idx] = v;
    }
    void deleteLineOfList(const Var &index){
        /* index: 1-origined */
        string kwd = index.asString();
        if (kwd == "all"){
            data.clear();
        }else if (kwd == "last"){
            data.pop_back();
        }else{
            int idx = (int)index.asNumber() - 1;
            if (0 <= idx && idx < data.size()) data.erase(data.begin() + idx);
        }
    }
    void insertAtIndexOfList(const Var &item, const Var &index){
        /* index: 1-origined */
        int idx = (int)index.asNumber() - 1;
        if (0 <= idx && idx <= data.size()) data.insert(data.begin() + idx, item);   
    }
    void insertAtRandomOfList(const Var &item){
        int idx = rand() % (data.size() + 1);
        data.insert(data.begin() + idx, item);
    }
    string asString() const{
        /* concatenate elements of list with space */
        // TODO: concatenated without spaces only if all elements are single characters.
        // (Is it an official bug? (or feature?))
        string ret;
        for(int i=0;i<data.size();i++){
            if (i > 0) ret += ' ';
            ret += data[i].asString();
        }
        return ret;        
    }
    int itemNumOfList(const Var &item) const{
        auto itr = find(data.begin(), data.end(), item);
        if (itr == data.end()) return 0;
        return 1 + (int)(itr - data.begin());
        /* index: 1-origined */
    }
    friend ostream& operator << (ostream& os, const VarList& p);
};
ostream& operator << (ostream& os, const VarList& p){
    os << p.asString();
    return os;
}

long double randUniform(const long double x, const long double y){
    if (x > y) return randUniform(y, x);
    if (floor(x) == x && floor(y) == y){
        ll xi = (ll)round(x), yi = (ll)round(y);
        return xi + rand() % (yi - xi + 1);
    }else{
        return x + (y - x) * (0.0 + rand()) / RAND_MAX;
    }
}

Var buf_answer; // for "answer"

// ============================= Scripts =============================

// variable declaration
Var var_n(3);
Var var_div(4);
Var var_seg(5);
Var var_fb("1");
Var var_k(4);
Var var_sb(3);
Var var_fe(3);
Var var_se(4);
Var var_i(2);
Var var_j(4);
Var var_p(4);
Var var_N("3");
Var var_M(2);
Var var_ans(5);
Var var_buy("4");

// list declaration
VarList list_tmp({Var("1"), Var("1"), Var("1")});
VarList list_ary({Var("1"), Var("1"), Var("1")});
VarList list_A({});
VarList list_B({Var("3"), Var("4"), Var("5")});
VarList list_ary__idx({Var("1"), Var(2), Var(3)});
VarList list_tmp__idx({Var("1"), Var(2), Var(3)});

// prototype declaration of functions
int func_merge__sort__ary();
int main();

// contents of functions
int func_merge__sort__ary(){
    var_n = Var(list_ary.size());
    list_tmp.deleteLineOfList(Var("all"));
    list_tmp__idx.deleteLineOfList(Var("all"));
    list_ary__idx.deleteLineOfList(Var("all"));
    var_i = Var("1");
    for (int cnt_0=0;cnt_0<var_n.asNumber();cnt_0++){
        list_ary__idx.push_back(var_i);
        list_tmp.push_back(Var("0"));
        list_tmp__idx.push_back(Var("0"));
        var_i += Var("1");
    }
    var_n += Var("1");
    var_div = Var("1");
    while (!(!(var_div < var_n))){
        var_seg = Var("1");
        while (!(!(var_seg < var_n))){
            var_fb = var_seg;
            var_k = var_seg;
            if ((((var_fb + var_div) < var_n) || ((var_fb + var_div) == var_n))){
                var_sb = (var_fb + var_div);
                var_fe = (var_fb + var_div);
            } else {
                var_sb = var_n;
                var_fe = var_n;
            }
            if ((((var_sb + var_div) < var_n) || ((var_sb + var_div) == var_n))){
                var_se = (var_sb + var_div);
            } else {
                var_se = var_n;
            }
            var_i = var_fb;
            var_j = var_sb;
            while (!(!((var_i < var_fe) && (var_j < var_se)))){
                if (((list_ary.getLineOfList(var_i) < list_ary.getLineOfList(var_j)) || (list_ary.getLineOfList(var_i) == list_ary.getLineOfList(var_j)))){
                    list_tmp.setLineOfListTo(var_k, list_ary.getLineOfList(var_i));
                    list_tmp__idx.setLineOfListTo(var_k, list_ary__idx.getLineOfList(var_i));
                    var_i += Var("1");
                } else {
                    list_tmp.setLineOfListTo(var_k, list_ary.getLineOfList(var_j));
                    list_tmp__idx.setLineOfListTo(var_k, list_ary__idx.getLineOfList(var_j));
                    var_j += Var("1");
                }
                var_k += Var("1");
            }
            while (!(!(var_i < var_fe))){
                list_tmp.setLineOfListTo(var_k, list_ary.getLineOfList(var_i));
                list_tmp__idx.setLineOfListTo(var_k, list_ary__idx.getLineOfList(var_i));
                var_k += Var("1");
                var_i += Var("1");
            }
            while (!(!(var_j < var_se))){
                list_tmp.setLineOfListTo(var_k, list_ary.getLineOfList(var_j));
                list_tmp__idx.setLineOfListTo(var_k, list_ary__idx.getLineOfList(var_j));
                var_k += Var("1");
                var_j += Var("1");
            }
            var_p = var_seg;
            while (!(!(var_p < var_k))){
                list_ary.setLineOfListTo(var_p, list_tmp.getLineOfList(var_p));
                list_ary__idx.setLineOfListTo(var_p, list_tmp__idx.getLineOfList(var_p));
                var_p += Var("1");
            }
            var_seg = (var_seg + (var_div * Var("2")));
        }
        var_div = (var_div * Var("2"));
    }
    var_n += Var("-1");
    return 0;
}

int main(){
    list_ary.clear();
    list_A.clear();
    list_B.clear();
    cin >> buf_answer;
    var_N = buf_answer;
    cin >> buf_answer;
    var_M = buf_answer;
    for (int cnt_1=0;cnt_1<var_N.asNumber();cnt_1++){
        cin >> buf_answer;
        list_ary.push_back(buf_answer);
        cin >> buf_answer;
        list_B.push_back(buf_answer);
    }
    func_merge__sort__ary();
    var_ans = Var("0");
    var_i = Var("1");
    for (int cnt_2=0;cnt_2<var_N.asNumber();cnt_2++){
        var_buy = list_B.getLineOfList(list_ary__idx.getLineOfList(var_i));
        if ((var_buy < var_M)){
            var_ans += (list_ary.getLineOfList(var_i) * var_buy);
            var_M += (Var("0") - var_buy);
        } else {
            var_ans += (list_ary.getLineOfList(var_i) * var_M);
            cout << var_ans << endl;
            return 0;
        }
        var_i += Var("1");
    }
    return 0;
}