#include <bits/stdc++.h>
using namespace std;
struct node {
  int x, y;
};
node arr[100005];
bool cmp(node a, node b) { return a.x < b.x; }
int main() {
  int n, l, a;
  scanf("%d%d%d", &n, &l, &a);
  for (int i = 0; i < n; ++i) scanf("%d%d", &arr[i].x, &arr[i].y);
  int cnt = 0;
  sort(arr, arr + n, cmp);
  if (n == 0) {
    printf("%d\n", l / a);
    return 0;
  }
  cnt += arr[0].x / a;
  for (int i = 1; i < n; ++i) {
    cnt += (arr[i].x - arr[i - 1].y - arr[i - 1].x) / a;
  }
  cnt += (l - arr[n - 1].y - arr[n - 1].x) / a;
  printf("%d\n", cnt);
}
