#include <functional>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstring>
#include <string>
#include <vector>
#include <random>
#include <bitset>
#include <queue>
#include <cmath>
#include <stack>
#include <set>
#include <map>
typedef long long ll;
using namespace std;
const ll MOD = 1000000007LL;

template <typename T, typename E>
class LazySegmentTree {
    using F = function<T(T, T)>;
    using G = function<T(T, E)>;
    using H = function<E(E, E)>;
    int n, height;
    F f;
    G g;
    H h;
    T t;
    E e;
    vector<T> dat;
    vector<E> laz;

public:
    LazySegmentTree(F f, G g, H h, T t, E e): f(f), g(g), h(h), t(t), e(e) {}

    void init(int n_) {
        n = 1;
        height = 0;
        while (n < n_) { n <<= 1; height++; }
        dat.assign(2 * n, t);
        laz.assign(2 * n, e);
    }

    void build(const vector<T> &v) {
        auto n_ = (int)v.size();
        init(n_);
        for (int i = 0; i < n_; i++) dat[n + i] = v[i];
        for (int i = n - 1; i > 0; i--) dat[i] = f(dat[(i << 1) | 0], dat[(i << 1) | 1]);
    }

    inline T reflect(int k) {
        return laz[k] == e ? dat[k] : g(dat[k], laz[k]);
    }

    inline void eval(int k) {
        if (laz[k] == e) return;
        laz[(k << 1) | 0] = h(laz[(k << 1) | 0], laz[k]);
        laz[(k << 1) | 1] = h(laz[(k << 1) | 1], laz[k]);
        dat[k] = reflect(k);
        laz[k] = e;
    }

    inline void thrust(int k) {
        for (int i = height; i > 0; i--) {
            eval(k >> i);
        }
    }

    inline void recalc(int k) {
        while (k >>= 1) {
            dat[k] = f(reflect((k << 1) | 0), reflect((k << 1) | 1));
        }
    }

    void update(int a, int b, E x) {
        thrust(a += n);
        thrust(b += n - 1);
        for (int l = a, r = b + 1; l < r; l >>= 1, r >>= 1) {
            if (l & 1) laz[l] = h(laz[l], x), l++;
            if (r & 1) --r, laz[r] = h(laz[r], x);
        }
        recalc(a);
        recalc(b);
    }

    void set_val(int a, T x) {
        thrust(a += n);
        dat[a] = x;
        laz[a] = e;
        recalc(a);
    }

    T query(int a, int b) {
        thrust(a += n);
        thrust(b += n - 1);
        T vl = t, vr = t;
        for (int l = a, r = b + 1; l < r; l >>= 1, r >>= 1) {
            if (l & 1) vl = f(vl, reflect(l++));
            if (r & 1) vr = f(reflect(--r), vr);
        }
        return f(vl, vr);
    }
};

int main() {
    cin.sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    ll n, d, a;
    cin >> n >> d >> a;

    using P = pair<ll, ll>;
    vector <P> xh(n);
    for (int i = 0; i < n; i++) {
        ll x, h;
        cin >> x >> h;
        h = (h + a - 1) / a;
        xh[i] = P(x, h);
    }

    sort(xh.begin(), xh.end());

    vector <int> x(n);
    for (int i = 0; i < n; i++) x[i] = xh[i].first;

    // 区間add, 区間sum
    auto f = [](P a, P b) { return P(a.first + b.first, a.second + b.second); };
    auto g = [](P a, ll b) { return P(a.first + b * a.second, a.second); };
    auto h = [](ll a, ll b) { return a + b; };

    LazySegmentTree<P, ll> seg(f, g, h, P(0, 0), 0);
    seg.build(vector<P>(n, P(0, 1)));

    for (int i = 0; i < n; i++) {
        seg.update(i, i + 1, xh[i].second);
    }

    ll ans = 0;
    for (int i = 0; i < n; i++) {
        int cnt = seg.query(i, i + 1).first;
        if (cnt <= 0) continue;

        ans += cnt;

        ll op = xh[i].first + 2 * d;
        int idx = upper_bound(x.begin(), x.end(), op) - x.begin();

        seg.update(i, idx, -cnt);
    }

    cout << ans << "\n";
    return 0;
}

Measured memory_bytes: 19584