#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  long long p, m;
  scanf("%d%lld%lld", &n, &p, &m);
  long long curd = 1;
  long long curb = 0;
  long long sum = 0;
  for (int i = 0; i < n; ++i) {
    long long d, v;
    scanf("%lld%lld", &d, &v);
    long long tpos = 0;
    if (curb > 0) tpos = curb / p;
    if (curd + tpos < d) {
      sum += d - curd - tpos;
    }
    curb = curb - (d - curd) * p + v;
    curd = d;
  }
  long long tpos = 0;
  if (curb > 0) tpos = curb / p;
  if (curd + tpos <= m) {
    sum += m + 1 - curd - tpos;
  }
  printf("%lld\n", sum);
  return 0;
}
