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

using namespace std;

deque<long long> d;

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

    int n,s,t, pret = 0, c[100000] = {0},p[100000] = {0};
    f>>n>>s>>t;

    for(int i=0; i<n; i++)
    {
        f>>c[i]>>p[i];
        while(d.empty() == 1 && c[d.back()] + (i - d.back()) * s >= c[i])
            d.pop_back();

        while(d.empty() == 1 && (i - d.front()) > t)
            d.pop_front();
        d.push_back(i);
        pret += c[d.front()] * p[i] + p[i] * (i - d.front()) * s;
    }

    g<<pret;
    return 0;
}