#include <bits/stdc++.h>
using namespace std;
int n, m;
long long p;
pair<int, int> d[100011];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> p >> m;
  for (int i = 1; i <= n; i++) cin >> d[i].first >> d[i].second;
  if (d[n].first != m) {
    d[n + 1].first = m, d[n + 1].second = 0;
    n++;
  }
  long long cur = -p, ans = 1, cur_day = 2, st_i = 1;
  if (d[1].first == 1) {
    cur += d[1].second;
    if (cur >= 0) ans = 0;
    st_i = 2;
  }
  for (int i = st_i; i <= n; i++) {
    int L = cur_day, R = d[i].first - 1;
    if (cur_day == d[i].first) {
      cur += d[i].second - p;
      if (cur < 0) ans++;
      cur_day = d[i].first + 1;
      continue;
    }
    long long st_day = -1;
    while (L <= R) {
      int M = (L + R) / 2;
      long long x = cur - p * (M - cur_day + 1);
      if (x < 0) {
        st_day = M;
        R = M - 1;
      } else {
        L = M + 1;
      }
    }
    if (st_day != -1) {
      ans += (d[i].first - st_day);
    }
    cur -= p * (d[i].first - cur_day + 1);
    cur += d[i].second;
    if (cur < 0) ans++;
    cur_day = d[i].first + 1;
  }
  cout << ans;
  return 0;
}
