#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "debug.h"
#else
#define dump(...)
#endif
#define endl "\n"
#define ll long long
#define int ll
#define FOR(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define REP(i, x) for (int i = 0; i < (int)(x); i++)
#define REPS(i, x) for (int i = 1; i <= (int)(x); i++)
#define RREP(i, x) for (int i = ((int)(x)-1); i >= 0; i--)
#define RREPS(i, x) for (int i = ((int)(x)); i > 0; i--)
#define INF (1 << 30)
#define LLINF (1LL << 60)
#define vi vector<int>
#define vvi vector<vector<int>>
#define pi pair<int, int>
#define ALL(a) (a).begin(), (a).end()
#define BIT(n) (1LL << (n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end()) //sortしてからつかうこと
constexpr ll MOD = 1e9 + 7;
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, 1, -1, 1, -1};
ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
string S, T;
ll ans = 0;

template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec)
        is >> x;
    return is;
}

struct LazySegmentTree {
private:
public:
    int n;
    vector<ll> node, lazy;

    LazySegmentTree(vector<ll> v) {
        int sz = (int)v.size();
        n = 1;
        while (n < sz)
            n *= 2;
        node.resize(2 * n - 1);
        lazy.resize(2 * n - 1, 0);

        for (int i = 0; i < sz; i++)
            node[i + n - 1] = v[i];
        for (int i = n - 2; i >= 0; i--)
            node[i] = node[i * 2 + 1] + node[i * 2 + 2];
    }

    void eval(int k, int l, int r) {
        if (lazy[k] != 0) {
            node[k] += lazy[k];
            if (r - l > 1) {
                lazy[2 * k + 1] += lazy[k] / 2;
                lazy[2 * k + 2] += lazy[k] / 2;
            }
            lazy[k] = 0;
        }
    }

    void add(int a, int b, ll x, int k = 0, int l = 0, int r = -1) {
        if (r < 0)
            r = n;
        eval(k, l, r);
        if (b <= l || r <= a)
            return;
        if (a <= l && r <= b) {
            lazy[k] += (r - l) * x;
            eval(k, l, r);
        } else {
            add(a, b, x, 2 * k + 1, l, (l + r) / 2);
            add(a, b, x, 2 * k + 2, (l + r) / 2, r);
            node[k] = node[2 * k + 1] + node[2 * k + 2];
        }
    }

    ll getsum(int a, int b, int k = 0, int l = 0, int r = -1) {
        if (r < 0)
            r = n;
        eval(k, l, r);
        if (b <= l || r <= a)
            return 0;
        if (a <= l && r <= b)
            return node[k];
        ll vl = getsum(a, b, 2 * k + 1, l, (l + r) / 2);
        ll vr = getsum(a, b, 2 * k + 2, (l + r) / 2, r);
        return vl + vr;
    }
};

ll intceil(ll a, ll b) {
    return (a + (b - 1)) / b;
}

signed main() {
    cin >> N >> D >> A;
    vector<pair<ll, ll>> xh(N);
    vector<ll> x(N), h(N);
    for (int i = 0; i < N; i++) {
        cin >> xh[i].first >> xh[i].second;
    }
    sort(ALL(xh));
    for (int i = 0; i < N; i++) {
        x[i] = xh[i].first;
        h[i] = xh[i].second;
    }
    LazySegmentTree seg(h);
    for (int i = 0; i < N; i++) {
        int hp = seg.getsum(i, i + 1);
        if (hp <= 0) {
            continue;
        }
        auto itr = upper_bound(ALL(x), x[i] + 2 * D);
        int index = itr - x.begin();
        int n = intceil(hp, A);
        seg.add(i, index, -A * n);
        ans += n;
    }
    cout << ans << endl;
}

Measured memory_bytes: 16256