#include <bits/stdc++.h>
using namespace std;
void input(long long int n, long long int a[]) {
  for (long long int i = 0; i < n; ++i) cin >> a[i];
}
long long int bin_expo(long long int A, long long int B, long long int M) {
  long long int res = 1LL;
  while (B > 0) {
    if (B % 2 == 1) {
      res = (res * A) % M;
    }
    A = (A * A) % M;
    B = B / 2;
  }
  return res;
}
bool isPrime[100 + 1];
void sieve() {
  long long int i, j;
  memset(isPrime, true, sizeof(isPrime));
  isPrime[1] = false;
  isPrime[0] = false;
  for (i = 2; i * i <= 100; i++) {
    if (isPrime[i] == true) {
      for (j = i * i; j <= 100; j = j + i) isPrime[j] = false;
    }
  }
}
long long int gcd(long long int a, long long int b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long int lcm(long long int a, long long int b) {
  return (a * b) / gcd(a, b);
}
long double distance(long long int x1, long long int y1, long long int x2,
                     long long int y2) {
  return sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2) * 1.0);
}
void getDigits(long long x, vector<int> &digit) {
  while (x) {
    digit.push_back(x % 10);
    x /= 10;
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  long long int n, l, m, x, y;
  cin >> n >> l >> m;
  if (n == 0) {
    cout << l / m << endl;
    return 0;
  }
  pair<long long int, long long int> p[n];
  for (int i = 0; i < n; i++) {
    cin >> x >> y;
    p[i] = {x, x + y};
  }
  long long int ans = 0;
  long long int tmp = p[0].first;
  ans += tmp / m;
  for (int i = 1; i < n; i++) {
    tmp = p[i].first - p[i - 1].second;
    ans += tmp / m;
  }
  tmp = l - p[n - 1].second;
  ans += tmp / m;
  cout << ans << endl;
  return 0;
}
