#include <iostream>
#include <fstream>
#include <deque>
int main()
{
    std::fstream f ("branza.in");
    std::ofstream g ("branza.out");
    long v[100000], n,s,t,a,tot=0;
    std::deque <int> deq;
    f>>n>>s>>t;
    for(int i=1;i<=n;i++){
        f>>v[i]>>a;
        while(!deq.empty() && v[i]<v[deq.back()] + s*(i-deq.back()))
            deq.pop_back();
        deq.push_back(i);
        while(!deq.empty() && i-deq.front()>t)
            deq.pop_front();
        tot=tot+a*(v[deq.front()]+s*(i-deq.front()));
    }
    g<<tot;

    f.close();
    g.close();
    return 0;
}