#include <iostream>
#include <fstream>
std::ifstream f("branza.in");
std::ofstream g("branza.out");

struct saptamana{
    long long c,p;
};
int main() {
    int n,s,t;
    long long suma = 0;
    f>>n>>s>>t;
    saptamana v[n+1];
    for(int i = 1; i <= n; i++){
        f>>v[i].c>>v[i].p;
    }

    for(int i = 1; i <= n; i++){
        suma = suma + v[i].c*v[i].p;
        for(int j = i+1; (j <= n && j <= i+t); j++){
            if(v[i].c + (s*(j-i)) <= v[j].c){
                suma += ((v[i].c+s*(j-i))*v[j].p);
                v[j].p = 0;
            }
            else j = n+1;
        }
    }
    g<<suma;
    return 0;
}