#include <iostream>
#include <deque>
#include <fstream>
using namespace std;
deque <pair<int, int>> branzeturi;
ifstream f("branza.in");
ofstream g("branza.out");

int main() {
    int N,S,T, cost, cantitate, costFinal = 0;
    //pair <int, int> ziCurenta;
    f>>N>>S>>T;
    for (int i = 1; i <= N; i++)
    {
        f>>cost>>cantitate;

        while(branzeturi.empty() != 1 && branzeturi.front().second < i - T)
            branzeturi.pop_front();
        while(branzeturi.empty() != 1 && ((i - branzeturi.back().first) * S + branzeturi.back().second) > cost)
            branzeturi.pop_back();

        branzeturi.push_back({i,cost});
        costFinal += cantitate * ((i - branzeturi.front().first) * S + branzeturi.front().second);
    }
    g<<costFinal;
    f.close();
    g.close();
    return 0;
}