#include <bits/stdc++.h>   using namespace std;   int main() {     long long int n, l, a, q[100001], w[100001], sum = 0, i;     cin >> n >> l >> a;     for (i = 0; i < n; i++) {       cin >> q[i] >> w[i];     }     if (n == 0) {       cout << l / a;       return 0;     }     sum = sum + q[0] / a;     for (i = 1; i < n; i++) {       sum = sum + (q[i] - w[i - 1] - q[i - 1]) / a;     }     sum = sum + (l - w[n - 1] - q[i - 1]) / a;     cout << sum;   }   