#include <bits/stdc++.h>
int main() {
  int n, i;
  long long p, m, t, add, last = 0, cur = 0, bel, wyn = 0;
  scanf("%d %lld %lld", &n, &p, &m);
  for (i = 0; i < n; i++) {
    scanf("%lld %lld", &t, &add);
    if (cur >= 0)
      bel = last + cur / p;
    else
      bel = last - 1;
    if (bel < t) wyn = wyn + t - bel - 1;
    cur = cur - (t - last) * p + add;
    last = t;
  }
  t = m + 1, add = 0;
  if (cur >= 0)
    bel = last + cur / p;
  else
    bel = last - 1;
  if (bel < t) wyn = wyn + t - bel - 1;
  printf("%lld", wyn);
  return 0;
}
