#include <bits/stdc++.h>
using namespace std;
using ull = unsigned long long;
using ll = long long;
const int N = 100005, MOD = 1e9 + 7;
int n, p, m;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  cin >> n >> p >> m;
  int ans = 0, ptr = 0;
  ll curr = 0;
  for (ll i = 0, d, t; i <= n; ++i) {
    if (i == n)
      d = m + 1, t = (ll)1e18;
    else
      cin >> d >> t;
    if (curr < 0) {
      ans += d - ptr - 1;
    } else {
      ll ddt = (curr / p) + 1;
      ans += max(0ll, (ll)d - ((ll)ptr + ddt));
    }
    curr -= (ll)(d - ptr) * p;
    curr += t;
    ptr = d;
    if (curr < 0) {
      ++ans;
    }
  }
  cout << ans << '\n';
  return 0;
}
