#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f ("branza.in");
ofstream g ("branza.out");
deque <pair<int,int>> coada;
int main()
{
    int N,S,T,C,P,i,pret_zi;
    long long cost=0;
    f>>N>>S>>T;
    for (i=1; i<=N; i++)
    {
        f>>C>>P;
        coada.push_back(make_pair(C,i));
        pret_zi=C*P;
        for (std::deque<pair<int,int>>::iterator it=coada.begin(); it!=coada.end(); ++it)
            if (pret_zi>(*it).first*P+P*S*(i-(*it).second) && i-(*it).second<T)
                pret_zi=(*it).first*P+P*S*(i-(*it).second);
        cost+=pret_zi;
    }
    g<<cost;
}