#include <fstream>

using namespace std;

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

const int VM = 1e5;
int d [VM + 1], pret [VM + 1];

int main() {
  long long n, s, t;
  long long cant, rez, st, dr;
  in >> n >> s >> t;
  rez = dr = 0; st = 1;
  for (int i = 1; i <= n; i ++) {
    in >> pret [i] >> cant;
    if (st <= dr && i - d [st] == t)
      st ++;
    while (st <= dr && pret [i] <= pret [d [dr]] + s * (i - d [dr]))
      dr --;
    d [++ dr] = i;
    rez += cant * (pret [d [st]] + s * (d [dr] - d [st]));
  }
  out << rez;
  return 0;
}