#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <numeric>
#include <utility>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <unordered_map>
using namespace std;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P)
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P)
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T> ostream& operator << (ostream &s, vector<vector<T> > P)
{ for (int i = 0; i < P.size(); ++i) { s << endl << P[i]; } return s << endl; }

#define EACH(i, s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)
template<class T> ostream& operator << (ostream &s, set<T> P)
{ EACH(it, P) { s << "<" << *it << "> "; } return s << endl; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P)
{ EACH(it, P) { s << "<" << it->first << "->" << it->second << "> "; } return s << endl; }

template<class T> vector<T> make_vec(size_t a) { return vector<T>(a); }
template<class T, class... Ts> auto make_vec(size_t a, Ts... ts) {
  return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}
template<class T, class V>
typename enable_if<is_class<T>::value == 0>::type fill(T &t, const V &v) {
    t = v;
}
template<class T, class V>
typename enable_if<is_class<T>::value != 0>::type fill(T &t, const V &v){
    for (auto &e : t) fill(e, v);
}


template<class Monoid, class Action> struct SegTree {
    using FuncMonoid = function< Monoid(Monoid, Monoid) >;
    using FuncAction = function< void(Monoid&, Action) >;
    using FuncLazy = function< void(Action&, Action) >;
    FuncMonoid FM;
    FuncAction FA;
    FuncLazy FL;
    Monoid UNITY_MONOID;
    Action UNITY_LAZY;
    int SIZE, HEIGHT;
    vector<Monoid> dat;
    vector<Action> lazy;
    
    SegTree() { }
    SegTree(int n, const FuncMonoid fm, const FuncAction fa, const FuncLazy fl,
            const Monoid &unity_monoid, const Action &unity_lazy)
    : FM(fm), FA(fa), FL(fl), UNITY_MONOID(unity_monoid), UNITY_LAZY(unity_lazy) {
        SIZE = 1; HEIGHT = 0;
        while (SIZE < n) SIZE <<= 1, ++HEIGHT;
        dat.assign(SIZE * 2, UNITY_MONOID);
        lazy.assign(SIZE * 2, UNITY_LAZY);
    }
    void init(int n, const FuncMonoid fm, const FuncAction fa, const FuncLazy fl,
              const Monoid &unity_monoid, const Action &unity_lazy) {
        FM = fm; FA = fa; FL = fl;
        UNITY_MONOID = unity_monoid; UNITY_LAZY = unity_lazy;
        SIZE = 1; HEIGHT = 0;
        while (SIZE < n) SIZE <<= 1, ++HEIGHT;
        dat.assign(SIZE * 2, UNITY_MONOID);
        lazy.assign(SIZE * 2, UNITY_LAZY);
    }
    
    /* set, a is 0-indexed */
    void set(int a, const Monoid &v) { dat[a + SIZE] = v; }
    void build() {
        for (int k = SIZE - 1; k > 0; --k)
            dat[k] = FM(dat[k*2], dat[k*2+1]);
    }
    
    /* update [a, b) */
    inline void evaluate(int k) {
        if (lazy[k] == UNITY_LAZY) return;
        if (k < SIZE) FL(lazy[k*2], lazy[k]), FL(lazy[k*2+1], lazy[k]);
        FA(dat[k], lazy[k]);
        lazy[k] = UNITY_LAZY;
    }
    inline void update(int a, int b, const Action &v, int k, int l, int r) {
        evaluate(k);
        if (a <= l && r <= b)  FL(lazy[k], v), evaluate(k);
        else if (a < r && l < b) {
            update(a, b, v, k*2, l, (l+r)>>1), update(a, b, v, k*2+1, (l+r)>>1, r);
            dat[k] = FM(dat[k*2], dat[k*2+1]);
        }
    }
    inline void update(int a, int b, const Action &v) { update(a, b, v, 1, 0, SIZE); }
    
    /* get [a, b) */
    inline Monoid get(int a, int b, int k, int l, int r) {
        evaluate(k);
        if (a <= l && r <= b)
            return dat[k];
        else if (a < r && l < b)
            return FM(get(a, b, k*2, l, (l+r)>>1), get(a, b, k*2+1, (l+r)>>1, r));
        else
            return UNITY_MONOID;
    }
    inline Monoid get(int a, int b) { return get(a, b, 1, 0, SIZE); }
    inline Monoid operator [] (int a) { return get(a, a+1); }
    
    /* debug */
    void print() {
        for (int i = 0; i < SIZE; ++i) { cout << (*this)[i]; if (i != SIZE) cout << ","; }
        cout << endl;
    }
};

using pll = pair<long long, long long>;
int N;
long long D, A;
vector<long long> X, H;

long long solve() {
    vector<int> ids(N);
    for (int i = 0; i < N; ++i) ids[i] = i;
    sort(ids.begin(), ids.end(), [&](int i, int j) {
            return X[i] < X[j]; });
    vector<long long> nX(N), nH(N);
    for (int i = 0; i < N; ++i) nX[i] = X[ids[i]], nH[i] = H[ids[i]];
    X = nX, H = nH;
    
    auto fm = [](long long a, long long b) { return min(a, b); };
    auto fa = [](long long &a, long long d) { a += d; };
    auto fl = [](long long &d, long long e) { d += e; };
    SegTree<long long, long long> seg(N+10, fm, fa, fl, (1LL<<60), 0);

    //COUT(X); COUT(H);
    
    for (int i = 0; i < N; ++i) seg.set(i, H[i]);
    seg.build();

    long long res = 0;
    for (int i = 0; i < N; ++i) {
        long long cur = seg.get(i, i+1);
        if (cur <= 0) continue;
        long long need = (cur + A - 1) / A;
        long long right = X[i] + D * 2;
        int id = upper_bound(X.begin(), X.end(), right) - X.begin();
        //--id;
        seg.update(i, id, -need * A);
        res += need;

        /*
        COUT("--------------");
        COUT(i); COUT(cur); COUT(right); COUT(id); COUT(need);
        seg.print();
        */
    }
    return res;
}

int main() {
    //ios::sync_with_stdio(false);
    //cin.tie(0);

    while (cin >> N >> D >> A) {
        X.resize(N); H.resize(N);
        for (int i = 0; i < N; ++i) cin >> X[i] >> H[i];
        cout << solve() << endl;
    }
}


















Measured memory_bytes: 16768