#include <deque>
#include <fstream>
#include <iostream>
using namespace std;

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

const int MAX_N = 10100;
typedef long long int64;

int64 N, S, T;
int64 C[MAX_N], P[MAX_N];
deque<pair<int64, int64> > dq;

int main() {
  fin >> N >> S >> T;

  int64 answer = 0;
  for (int i = 1; i <= N; ++i) {
    fin >> C[i] >> P[i];
    if (!dq.empty() && i - dq.front().second > T) {
      dq.pop_front();
    }
    while (!dq.empty() && dq.back().first + (i - dq.back().second) * S > C[i]) {
      dq.pop_back();
    }
    dq.push_back(make_pair(C[i], i));

    answer += dq.front().first * P[i] * 1LL +
              S * (i - dq.front().second) * P[i] * 1LL;
  }

  fout << answer;
  return 0;
}