#include <bits/stdc++.h>
using namespace std;
long long n, m, p, c, d[100001], t[100001], ans;
int main() {
  scanf("%I64d%I64d%I64d", &n, &p, &m);
  for (int i = 1; i <= n + 1; i++) {
    if (i <= n)
      scanf("%I64d%I64d", &d[i], &t[i]);
    else
      d[i] = m;
    if (d[i] == d[i - 1]) break;
    long long k = max(0ll, c / p);
    ans += max(0ll, d[i] - d[i - 1] - k - 1);
    c = c - (d[i] - d[i - 1]) * p + t[i];
    if (c < 0) ans++;
  }
  printf("%I64d\n", ans);
  return 0;
}
