#include <iostream>
#include<fstream>
#include<deque>

using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");
deque<int> d;

int main()
{
    long long n,s,t,p,c[100010], pret = 0;
    f>>n>>s>>t;
    t++;

    for(int i =0; i<n;i++)
    {
        f>>c[i]>>p;

        if(d.size() != 0 && d.front() == i-t)
            d.pop_front();

        while(d.size() != 0 && c[i] <= c[d.back()]+ s* (i - d.back()))
            d.pop_back();
        d.push_back(i);

        pret += (long long)p * (c[d.front()] + s* (i - d.front()));
    }
    g<<pret;

    return 0;
}