#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

template <class Monoid, class OpMonoid>
class LazySegmentTree {
  using FuncMM = std::function<Monoid(Monoid, Monoid)>;
  using FuncMO = std::function<Monoid(Monoid, OpMonoid, int)>;
  using FuncOO = std::function<OpMonoid(OpMonoid, OpMonoid)>;

  const FuncMM funcMM;
  const FuncMO funcMO;
  const FuncOO funcOO;
  const Monoid monoidIdentity;
  const OpMonoid opMonoidIdentity;

  int N;
  std::vector<Monoid> dat;
  std::vector<OpMonoid> lazy;

  void setLazy(int k, const OpMonoid& om) { lazy[k] = funcOO(lazy[k], om); }
  void push(int k, int len) {
    if (lazy[k] == opMonoidIdentity) return;
    if (k < N) {
      setLazy(2 * k + 0, lazy[k]);
      setLazy(2 * k + 1, lazy[k]);
    }
    dat[k] = funcMO(dat[k], lazy[k], len);
    lazy[k] = opMonoidIdentity;
  }

 public:
  LazySegmentTree(int n, const FuncMM funcMM, const FuncMO funcMO,
                  const FuncOO funcOO, const Monoid monoidIdentity,
                  const OpMonoid opMonoidIdentity)
      : funcMM(funcMM),
        funcMO(funcMO),
        funcOO(funcOO),
        monoidIdentity(monoidIdentity),
        opMonoidIdentity(opMonoidIdentity) {
    N = 1;
    while (N < n) N *= 2;
    dat.resize(2 * N, monoidIdentity);
    lazy.resize(2 * N, opMonoidIdentity);
  }

  void dump() {
    std::cout << "dat: ";
    for (int i = 1; i < dat.size(); i++) {
      if (i == N) std::cout << "| ";
      std::cout << dat[i].ai << "(" << lazy[i].p << "," << lazy[i].q << ","
                << lazy[i].r << ") ";
    }
    std::cout << std::endl;
  }

  void set(int i, const Monoid& v) { dat[N + i] = v; }

  void init() {
    for (int i = N - 1; i > 0; i--) {
      dat[i] = funcMM(dat[2 * i + 0], dat[2 * i + 1]);
    }
  }

  void update(int s, int t, const OpMonoid& om) { update(s, t, om, 1, 0, N); }
  void update(int s, int t, const OpMonoid& om, int k, int l, int r) {
    push(k, r - l);
    if (r <= s || t <= l) return;
    if (s <= l && r <= t) {
      setLazy(k, om);
      push(k, r - l);
      return;
    }
    update(s, t, om, 2 * k + 0, l, (l + r) / 2);
    update(s, t, om, 2 * k + 1, (l + r) / 2, r);
    dat[k] = funcMM(dat[2 * k + 0], dat[2 * k + 1]);
  }

  Monoid query(int s, int t) { return query(s, t, 1, 0, N); }
  Monoid query(int s, int t, int k, int l, int r) {
    push(k, r - l);
    if (r <= s || t <= l) return monoidIdentity;
    if (s <= l && r <= t) return dat[k];
    Monoid vl = query(s, t, 2 * k + 0, l, (l + r) / 2);
    Monoid vr = query(s, t, 2 * k + 1, (l + r) / 2, r);
    return funcMM(vl, vr);
  }
};

struct VAL {
  ll ai;
};

struct OP {
  ll p;
};
bool operator==(const OP& a, const OP& b) {
  return a.p == b.p;
}


int main(){
  int N, D, A;
  cin >> N >> D >> A;
  vector<pair<ll,ll>> v;
  rep(i,N){
    ll x, h;
    cin >> x >> h;
    v.emplace_back(x,h);
  }

  sort(ALLOF(v));

  vector<int> range;
  int idx = 0;
  rep(i,N){
    while(idx+1 < N && v[idx+1].first <= v[i].first + 2*D) idx++;
    range.push_back(idx+1);
  }

  auto funcMM = [](const VAL& a, const VAL& b) {
    VAL ret;
    ret.ai = a.ai + b.ai;
    return ret;
  };
  auto funcMO = [](const VAL& a, const OP& b, int k) {
    VAL ret;
    ret.ai = (a.ai + b.p) * k;
    return ret;
  };
  auto funcOO = [](const OP& a, const OP& b) {
    OP ret;
    ret.p = b.p + a.p;
    return ret;
  };

  LazySegmentTree<VAL, OP> lst(N, funcMM, funcMO, funcOO, (VAL){0},
                               (OP){0});
  rep(i,N){
    VAL val;
    val.ai = v[i].second;
    lst.set(i, val);
  }
  ll ret = 0;
  rep(i,N){
    ll val = lst.query(i,i+1).ai;
    //cout << i << " " << val << endl;
    if(val <= 0) continue;
    ll damage = (val + A - 1) / A;
    OP op;
    op.p = -damage * A;
    lst.update(i,range[i],op);
    //cout << " " << i << " " << range[i] << " " << op.p << endl;
    ret += damage;
  }

  cout << ret << endl;
  
  return 0;
}


Measured memory_bytes: 13676