#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;

int n, d, a, x, h;
long long s, ans;
vector <pair<int, int> > v;
queue <pair<int, long long> > q;

int main(){
    cin >> n >> d >> a;
    for (int i = 0; i < n; i++){
        cin >> x >> h;
        v.push_back({x, (h-1)/a+1});
    }
    sort(v.begin(), v.end());
    for (int i = 0; i < n; i++){
        while (!q.empty() && q.front().second < v[i].first){
            s -= q.front().first;
            q.pop();
        }
        if (s < v[i].second){
            q.push({v[i].second-s, v[i].first+d*2});
            ans += v[i].second - s;
            s = v[i].second;
        }
    }
    cout << ans << "\n";
}
