#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T>
using V = vector<T>;
template <class T, class U>
using P = pair<T, U>;
using vll = V<ll>;
using vvll = V<vll>;
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
constexpr ll MOD = 1000000007;
constexpr ll HIGHINF = (ll)1e18;
constexpr int INF = 1e9;
using PI = P<ll, ll>;
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n, L, a;
  cin >> n >> L >> a;
  V<PI> tl(n);
  for (int i = 0; i < n; i++) cin >> tl[i].first >> tl[i].second;
  sort(tl.begin(), tl.end());
  tl.emplace_back(PI(L, 0));
  int prev = 0;
  ll ans = 0;
  for (int i = 0; i < n + 1; i++) {
    int bre = max(0LL, tl[i].first - ll(prev));
    ans += bre / a;
    prev = tl[i].first + tl[i].second;
  }
  cout << ans << '\n';
  return 0;
}
