#include"bits/stdc++.h"
using namespace std;
#define REP(k,m,n) for(int (k)=(m);(k)<(n);(k)++)
#define rep(i,n) REP((i),0,(n))
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using tp3 = tuple<int, int, int>;
using Mat = vector<vector<ll>>;
constexpr int INF = 1 << 28;
constexpr ll INFL = 1ll << 60;
constexpr int dh[4] = { 0,1,0,-1 };
constexpr int dw[4] = { -1,0,1,0 };
bool isin(const int H, const int W, const int h, const int w) {
    return 0 <= h && h < H && 0 <= w && w < W;
}
template<typename T>
T minch(T& l, T& r) {
    return l = min(l, r);
}
template<typename T>
T maxch(T& l, T& r) {
    return l = max(l, r);
}
template<typename T>
void output(const T& val) {
    cout << val << endl;
}
template<typename T>
void output(const vector<T>& vec, const bool newline = false) {
    for (const T& val : vec)cout << val << (newline ? '\n' : ' '); cout << endl;
}
template<typename T>
void output(const vector<vector<T>>& mat) {
    for (const auto& row : mat)output(row);
}
template<typename Monoid, typename OperatorMonoid = Monoid>
class LazySegmentTree {
private:
    using F = function<Monoid(Monoid, Monoid)>;
    using G = function<Monoid(Monoid, OperatorMonoid, int)>;
    using H = function<OperatorMonoid(OperatorMonoid, OperatorMonoid)>;

    int sz; // 対応する配列の幅
    vector<Monoid> data;
    vector<OperatorMonoid> lazy;
    const F f; // 2区間マージ演算(data-data-ボトムアップマージ)
    const G g; // 要素,作用素マージ演算(lazy->data同位置変換時の、(data,lazy,len)の計算)
    const H h; // 作用素マージ演算　(query->lazyトップダウン伝搬時の、(lazy,query_value)の計算)
    const Monoid M1;          // モノイド単位元　(data単位元)
    const OperatorMonoid OM0; // 作用素単位元 (lazy単位元)

    void propagate(int idx, int len) {
        // 幅lenのlazy[idx]が存在するとき、値を下に流す
        if (lazy[idx] != OM0) {
            if (idx < sz) {
                lazy[(idx << 1) | 0] = h(lazy[(idx << 1) | 0], lazy[idx]);
                lazy[(idx << 1) | 1] = h(lazy[(idx << 1) | 1], lazy[idx]);
            }
            data[idx] = g(data[idx], lazy[idx], len);
            lazy[idx] = OM0;
        }
    }
    Monoid update_impl(int a, int b, const OperatorMonoid& val, int idx, int l, int r) {
        propagate(idx, r - l);
        if (r <= a || b <= l)return data[idx];
        else if (a <= l && r <= b) {
            lazy[idx] = h(lazy[idx], val);
            propagate(idx, r - l);
            return data[idx];
        }
        else return data[idx] = f(
            update_impl(a, b, val, (idx << 1) | 0, l, (l + r) >> 1),
            update_impl(a, b, val, (idx << 1) | 1, (l + r) >> 1, r)
        );
    }
    Monoid query_impl(int a, int b, int idx, int l, int r) {
        propagate(idx, r - l);
        if (r <= a || b <= l)return M1;
        else if (a <= l && r <= b)return data[idx];
        else return f(
            query_impl(a, b, (idx << 1) | 0, l, (l + r) >> 1),
            query_impl(a, b, (idx << 1) | 1, (l + r) >> 1, r)
        );
    }

public:
    // init忘れに注意
    LazySegmentTree(int n, const F f, const G g, const H h,
        const Monoid& M1, const OperatorMonoid OM0)
        :f(f), g(g), h(h), M1(M1), OM0(OM0) {
        sz = 1;
        while (sz < n)sz <<= 1;
        data.assign(2 * sz, M1);
        lazy.assign(2 * sz, OM0);
    }
    void build(const vector<Monoid>& vals) {
        rep(idx, vals.size())data[idx + sz] = vals[idx];
        for (int idx = sz - 1; idx > 0; idx--) {
            data[idx] = f(data[(idx << 1) | 0], data[(idx << 1) | 1]);
        }
    }
    Monoid update(int a, int b, const OperatorMonoid& val) {
        return update_impl(a, b, val, 1, 0, sz);
    }
    Monoid query(int a, int b) {
        return query_impl(a, b, 1, 0, sz);
    }
    Monoid operator[](const int& idx) {
        return query(idx, idx + 1);
    }
};
// ============ template finished ============

int main()
{
    ll N, D, A;
    cin >> N >> D >> A;
    vector<pll> xh(N);
    rep(i, N)cin >> xh[i].first >> xh[i].second;
    D = 2 * D;
    sort(xh.begin(), xh.end());
    vector<ll> hs(N);
    rep(i, N)hs[i] = xh[i].second;

    auto f = [](ll l, ll r) {return l + r; };
    auto g = [](ll data, ll lazy, int len) {return data + lazy * len; };
    auto h = [](ll lazy, ll query) {return lazy + query; };
    LazySegmentTree<ll> lst(N, f, g, h, 0, 0);
    lst.build(hs);

    ll res = 0;
    rep(i, N) {
        ll hp = lst[i];
        //cerr << i << " : ";
        //rep(i, N)cerr << lst[i] << " ";
        //cerr << endl;
        if (hp <= 0)continue;
        ll times = (hp + A - 1) / A;
        ll damage = times * A;
        ll rside = xh[i].first + D;
        ll ridx = lower_bound(xh.begin(), xh.end(), make_pair(rside, INFL)) - xh.begin();
        res += times;
        lst.update(i, ridx, -damage);
    }
    //cerr << "fin: ";
    //rep(i, N)cerr << lst[i] << " ";
    //cerr << endl;
    //output("-------");
    output(res);
    return 0;
}


Measured memory_bytes: 13184