#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
deque <int> d;
int n, s, t, v[10000000], p, suma=0;
int main()
{
    f>>n>>s>>t;
    for(int i=1; i<=n; i++)
    {
        f>>v[i]>>p;
        while(!d.empty() && d.front()<i-t)
            d.pop_front();
        while(!d.empty() && v[i]<v[d.back()]+(i-d.back())*s)
            d.pop_back();
        d.push_back(i);
        suma=suma+p*(v[d.front()]+(i-d.front())*s);
    }
    g<<suma;
    f.close();
    g.close();
    return 0;
}