#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  long long p, m;
  cin >> p >> m;
  vector<pair<long long, long long> > bonus(n);
  for (int i = 0; i < n; i++) cin >> bonus[i].first >> bonus[i].second;
  bonus.push_back({m + 1, -1});
  long long ans = m;
  long long cost = 0;
  long long has = 0;
  for (int i = 0; i < n; i++) {
    long long day = bonus[i].first;
    has += bonus[i].second;
    long long cost = has - day * p;
    if (cost >= 0) {
      int d = min(bonus[i + 1].first - day, 1 + cost / p);
      ans -= d;
    }
  }
  cout << ans << endl;
  return 0;
}
