#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");

deque<long long> pret_minim;

int main()
{
    long long n, s, t, min = 0, c, p, k;
    f >> n >> s >>t;
    k = 0;
    for (int i=0; i<n; i++)
    {
        f >> c >> p;
        if(i-k>t && pret_minim.size()!=0)
            pret_minim.pop_front();
        while(pret_minim.front()+(i-k)*s > c && pret_minim.size()!=0)
        {
            k++;
            pret_minim.pop_front();
        }
        pret_minim.push_back(c);
        min = min + p*(pret_minim.front()+(i-k)*s );
        }
   g << min;
}