text: //小希的新工作
  #include <cstdio>
  #include <iostream>
  using namespace std;
  
  int main()
  {
      int ti, li, n, lastEnd = 0, i, j, l, a, count = 0;
      scanf("%d %d %d", &n, &l, &a);
      for (i = 0; i < n; i++)
      {
          scanf("%d %d", &ti, &li);
          count += (ti - lastEnd) / a;
          lastEnd = ti + li;
      }
      count += (l - lastEnd) / a;
      printf("%d", count);
  }