#include <bits/stdc++.h>
using namespace std;
const long double pi = 4 * atan((long double)1);
const long long mod = 1e9 + 7;
const long long inf = 922337203685477;
const long long nax = 1e5 + 5;
long long n, p, m;
long long d[nax], t[nax];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> n >> p >> m;
  for (long long i = 1; i <= n; i++) {
    cin >> d[i] >> t[i];
  }
  d[0] = 1;
  d[n + 1] = m + 1;
  long long cur = 0, ans = 0;
  for (long long i = 1; i <= n + 1; i++) {
    long long dif = 0;
    if (cur > 0) {
      dif = cur / p;
    }
    long long minus = d[i] - d[i - 1] - dif;
    if (minus < 0) {
      minus = 0;
    }
    ans += minus;
    cur -= (d[i] - d[i - 1]) * p;
    cur += t[i];
  }
  cout << ans << '\n';
}
