// >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define int ll
#define double ld
#define rep(i,n) for (int i = 0; i < (int)(n); i++)
#define rep1(i,n) for (int i = 1; i <= (int)(n); i++)
#define repR(i,n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i,n) for (int i = (int)(n); i >= 1; i--)
#define loop(i,a,B) for (int i = a; i B; i++)
#define loopR(i,a,B) for (int i = a; i B; i--)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fst first
#define snd second
#define INF (numeric_limits<int>::max()/2-1)
#ifdef LOCAL
#include "debug.hpp"
#define dump(...) cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] ", dump_impl(#__VA_ARGS__, __VA_ARGS__)
#define say(x) cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] " << x << endl
#define debug if (1)
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#endif
template <class T> using pque_max = priority_queue<T>;
template <class T> using pque_min = priority_queue<T, vector<T>, greater<T> >;
template <class T, class = typename T::iterator, class = typename enable_if<!is_same<T, string>::value>::type>
ostream& operator<<(ostream& os, T const& v) { bool f = true; for (auto const& x : v) os << (f ? "" : " ") << x, f = false; return os; }
template <class T, class = typename T::iterator, class = typename enable_if<!is_same<T, string>::value>::type>
istream& operator>>(istream& is, T &v) { for (auto& x : v) is >> x; return is; }
template <class T, class S> istream& operator>>(istream& is, pair<T,S>& p) { return is >> p.first >> p.second; }
struct IOSetup { IOSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); } } iosetup;
template <class F> struct FixPoint : private F {
    constexpr FixPoint(F&& f) : F(forward<F>(f)) {}
    template <class... T> constexpr auto operator()(T&&... x) const { return F::operator()(*this, forward<T>(x)...); }
};
struct MakeFixPoint {
    template <class F> constexpr auto operator|(F&& f) const { return FixPoint<F>(forward<F>(f)); }
};
#define MFP MakeFixPoint()|
#define def(name, ...) auto name = MFP [&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
    using type = vector<typename vec_impl<T,d-1>::type>;
    template <class... U> static type make_v(size_t n, U&&... x) { return type(n, vec_impl<T,d-1>::make_v(forward<U>(x)...)); }
};
template <class T> struct vec_impl<T,0> { using type = T; static type make_v(T const& x = {}) { return x; } };
template <class T, size_t d = 1> using vec = typename vec_impl<T,d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args&&... args) { return vec_impl<T,d>::make_v(forward<Args>(args)...); }
template <class T> void quit(T const& x) { cout << x << endl; exit(0); }
template <class T> constexpr bool chmin(T& x, T const& y) { if (x > y) { x = y; return true; } return false; }
template <class T> constexpr bool chmax(T& x, T const& y) { if (x < y) { x = y; return true; } return false; }
template <class It> constexpr auto sumof(It b, It e) { return accumulate(b,e,typename iterator_traits<It>::value_type{}); }
template <class T> int sz(T const& x) { return x.size(); }
template <class C, class T> int lbd(C const& v, T const& x) {
    return lower_bound(v.begin(), v.end(), x)-v.begin();
}
template <class C, class T> int ubd(C const& v, T const& x) {
    return upper_bound(v.begin(), v.end(), x)-v.begin();
}
// <<<
void reord(vector<int> const&) { }
template <class T, class... Args>
void reord(vector<int> const& idx, vector<T> &v, Args&&... args) {
    vector<T> t(v.size());
    rep (i,v.size()) t[i] = v[idx[i]];
    swap(v,t);
    reord(idx, forward<Args>(args)...);
}
// >>> coordinate compression
template <class T>
struct Compress {
    vector<T> v;
    bool ok = false;
    void add(T const& x) { ok = false; v.push_back(x); }
    template <class It>
    void add(It f, It l) { ok = false; copy(f,l,back_inserter(v)); }
    void init() { sort(all(v)); v.erase(unique(all(v)), v.end()); ok = true; }
    int size() const { return v.size(); }
    T operator[](int i) const { assert(ok); return v[i]; }
    int find(T const& x) const { assert(ok); auto it = lower_bound(all(v),x); assert(*it == x); return it-v.begin(); }
};
// <<<
// >>> lazy segment tree
template <class Handler>
struct LazySegtree : Handler {
    static int32_t btmbit(int64_t x) { return x ? __builtin_ctzll(x) : -1; }
//    static int32_t btmbit(int32_t x) { return x ? __builtin_ctz(x) : -1; }

    using Value = typename Handler::Value;
    using Lazy = typename Handler::Lazy;
    using Handler::unit_value; // () -> Value
    using Handler::unit_action; // () -> Lazy
    using Handler::merge; // (Value,Value) -> Value
    using Handler::act; // (Lazy,Lazy&,Value&) -> void

    vector<Value> v;
    vector<Lazy> lz;
    int n;
    mutable Lazy tmp;

    LazySegtree() {}
    template <class... T> LazySegtree(T&&... x) { init(forward<T>(x)...); }

    template <class F, class = decltype(declval<F>()(0))>
    void init(int n, F gen)  {
        assert(n >= 0); this->n = n;
        v.resize(2*n); lz.assign(n, unit_action());
        for (int i = 0; i < n; i++) v[n+i] = gen(i);
        for (int i = n-1; i >= 1; i--) v[i] = merge(v[2*i],v[2*i+1]);
    }
    void init(int n) { init(n, [&](int) { return unit_value(); }); }
    void init(int n, Value const& x) { init(n, [&](int) { return x; }); }
    void init(vector<Value> const& v) { init(v.size(), [&](int i) { return v[i]; }); }
    int size() const { return n; }


    void act(Lazy const& x, int i) { act(x, (i < n ? lz[i] : tmp), v[i]); }
    void flush(int k) {
        if (n <= k || lz[k] == unit_action()) return;
        act(lz[k], 2*k);
        act(lz[k], 2*k+1);
        lz[k] = unit_action();
    }
    void flush(int l, int r) {
        for (int p = __lg(l += n), q = __lg(r += n-1); q; --p,--q) {
            flush(l >> p); flush(r >> q);
        }
    }
    void build(int i) {
        i += n; i >>= btmbit(i);
        while (i >>= 1) v[i] = merge(v[2*i],v[2*i+1]);
    }
    Value get(int l, int r) {
        assert(0 <= l && l <= r && r <= n);
        flush(l,r);
        Value x = unit_value(), y = unit_value();
        for (l += n, r += n; l < r; l >>= 1, r >>= 1) {
            if (l&1) x = merge(x,v[l++]);
            if (r&1) y = merge(v[--r],y);
        }
        return merge(x,y);
    }
    void apply(int l, int r, Lazy const& x) {
        assert(0 <= l && l <= r && r <= n);
        flush(l,r);
        for (int a = l+n, b = r+n; a < b; a >>= 1, b >>= 1) {
            if (a&1) act(x, a++);
            if (b&1) act(x, --b);
        }
        build(l); build(r);
    }
    Value operator[](int i) const { return get(i); }
    Value get(int i) const {
        assert(0 <= i && i < n);
        Value x = v[i += n];
        while (i >>= 1) act(lz[i], tmp, x);
        return x;
    }
    void set(int i, Value const& x) {
        assert(0 <= i && i < n);
        for (int p = __lg(i += n); p; --p) flush(i >> p);
        for (v[i] = x; i >>= 1; ) v[i] = merge(v[2*i],v[2*i+1]);
    }
    vector<Value> dat() const {
        vector<Value> ret(size());
        for (int i = 0; i < size(); i++) ret[i] = get(i);
        return ret;
    }
};
// <<<

// handler
struct RangeMinAdd {
    using Value = int;
    using Lazy = int;
    constexpr static Value unit_value() { return INF; }
    constexpr static Lazy unit_action() { return 0; }
    constexpr static Value merge(Value x, Value y) { return min(x,y); }
    static void act(Lazy x, Lazy &y, Value &z) {
        y += x, z += x;
    }
};

int32_t main() {
    int n,d,a; cin >> n >> d >> a;
    vector<int> x(n),h(n);
    rep (i,n) cin >> x[i] >> h[i];

    {
        vector<int> idx(n);
        iota(all(idx),0);
        sort(all(idx), [&](int i, int j) { return x[i] < x[j]; });
        reord(idx,x,h);
    }

    LazySegtree<RangeMinAdd> seg(h);

    int cnt = 0;
    rep (i,n) {
        int now = seg.get(i);
        if (now <= 0) continue;
        int k = (now+a-1)/a;
        cnt += k;
        int ub = ubd(x, x[i]+2*d);
        seg.apply(i,ub,-a*k);
    }

    cout << cnt << endl;

}


Measured memory_bytes: 8108