#include <bits/stdc++.h>
using namespace std;
void quicksort(long long int number[], long long int c[], long long int first,
               long long int last) {
  int i, j, pivot, temp;
  if (first < last) {
    pivot = first;
    i = first;
    j = last;
    while (i < j) {
      while (number[i] <= number[pivot] && i < last) i++;
      while (number[j] > number[pivot]) j--;
      if (i < j) {
        temp = number[i];
        number[i] = number[j];
        number[j] = temp;
        temp = c[i];
        c[i] = c[j];
        c[j] = temp;
      }
    }
    temp = number[pivot];
    number[pivot] = number[j];
    number[j] = temp;
    quicksort(number, c, first, j - 1);
    quicksort(number, c, j + 1, last);
  }
}
int main() {
  long long int i, j, k, n, l, ans = 0, a, arr[100000], brr[100000];
  cin >> n >> l >> a;
  for (i = 0; i < n; i++) cin >> arr[i] >> brr[i];
  if (arr[0] - a >= 0) ans = arr[0] / a;
  for (i = 0; i < n - 1; i++) {
    if (arr[i + 1] - (brr[i] + arr[i]) >= a) {
      ans = ans + (arr[i + 1] - (brr[i] + arr[i])) / a;
    }
  }
  ans = ans + (l - (arr[n - 1] + brr[n - 1])) / a;
  if (n == 0) ans = l / a;
  cout << ans;
}
