#include <fstream>
#include <deque>

using namespace std;

ifstream fin("branza.in");
ofstream fout("branza.out");

int n,s,t;
int c,p;
long long sum;

struct branza
{
    long long cant,pret,zi;
}v[100005];

deque < branza > deck;

int main()
{
    fin>>n>>s>>t;
    for (int i=1;i<=n;i++) {
        fin>>v[i].pret>>v[i].cant;
        v[i].zi=i;
        }
    for (int i=1;i<=n;i++) {

        while (!deck.empty() && (long long)v[i].cant*v[i].pret<(long long)v[i].cant*(deck.back().pret+(i-deck.back().zi)*s)) deck.pop_back();
        while (!deck.empty() && i-deck.front().zi>t) deck.pop_front();
        deck.push_back(v[i]);
        sum=sum+(long long)v[i].cant*(deck.front().pret+(i-deck.front().zi)*s);
    }
    fout<<sum;
}