#include <iostream>
#include <fstream>
using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
struct br{
    int c,p;
}v[100001];
int s,t,pret,n;
void calcul(int zi)
{
    int i,min=10000000;
    for(i=zi;i>0 && zi-i<t;i--)
        if(v[i].c+(zi-i)*s<min)
            min=v[i].c+(zi-i)*s;
    pret+=min*v[zi].p;

}
int main()
{
    int i;
    in>>n>>s>>t;
    for(i=1;i<=n;i++)
        in>>v[i].c>>v[i].p;
    for(i=n;i>0;i--)
        calcul(i);
    out<<pret;
}