#include <iostream>
#include <fstream>
#include <set>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
const int maxn = 100005;
multiset<int> diff;
int C[maxn];
int P[maxn];
int main() {
  int n, S, t;
  f >> n >> S >> t;
  for (int i = 1; i <= n; i++)
    f >> C[i] >> P[i];
  long long ans = 0;
  for (int i = 3; i <= n; i++) {
    diff.insert(C[i] - i * S);
    if (i > t)
      diff.erase(C[i - t] - (i - t));
    int aux = *diff.begin();
    ans = ans + P[i] * (i * S + aux);
  }
  g << ans << "\n";
  return 0;
}