#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long ll;

int main() {
    ios_base::sync_with_stdio(false);
    int n;
    ll R, D;
    cin >> n >> R >> D;

    vector<pair<ll, ll>> discos(n);

    for(int i = 0; i < n; i++) {
        cin >> discos[i].first >> discos[i].second;
    }

    sort(discos.begin(), discos.end());
    ll total_R = 2 * R;

    vector<pair<ll, ll>> q;
    q.reserve(n);
    ll active = 0, total = 0;
    int F =0 ;
    for(int i = 0; i < n; i++) {
        ll pos = discos[i].first, y = discos[i].second;
        ll need = (y + D - 1) / D;

        while(F < (int) q.size() and q[F].first < pos) {
            active -= q[F].second;
            F++;
        }

        if(need > active) {
            ll add = need - active;
            total += add;
            q.push_back(make_pair(pos + total_R, add));
            active += add;
        }
    }

    cout << total << endl;
    return 0;
}