#ifdef LOCAL
    #define _GLIBCXX_DEBUG
    #define __clock__
#else
    #pragma GCC optimize("Ofast")
#endif
#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using VI = vector<ll>;
using VV = vector<VI>;
using VS = vector<string>;
using PII = pair<ll, ll>;

// tourist set
template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char* s) {
  return to_string((string) s);
}

string to_string(bool b) {
  return (b ? "true" : "false");
}

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << '\n'; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// tourist set end

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

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define rep(i,b) FOR(i, 0, b)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<'\n'
#define p2(s, t) cout << (s) << " " << (t) << '\n'
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << '\n'
#define p_yes() p("YES")
#define p_no() p("NO")
#define SZ(x) ((int)(x).size())
#define SORT(A) sort(ALL(A))
#define RSORT(A) sort(ALL(A), greater<ll>())
#define MP make_pair

void no(){p_no(); exit(0);}
void yes(){p_yes(); exit(0);}

const ll mod = 1e9 + 7;
const ll inf = 1e18;
const double PI = acos(-1);

// ei1333's BIT
struct BIT {
  VI data;
  BIT(){}
  BIT(ll sz) {
    resize(sz);
  }
  void resize(ll sz){
    data.assign(++sz, 0);
  }
  ll sum(ll k) {
    ll ret = 0;
    for(++k; k > 0; k -= k & -k) ret += data[k];
    return (ret);
  }
  void add(ll k, ll x) {
    for(++k; k < (ll)data.size(); k += k & -k) data[k] += x;
  }
};
 
// 区間更新(加算)・区間和
struct Range{
  BIT P, Q;
  Range(ll sz){
    P.resize(sz+1);
    Q.resize(sz+1);
  }
  // [a, b)
  void update(ll a, ll b, ll w){
    P.add(a, -w*a);
    P.add(b,  w*b);
    Q.add(a,  w);
    Q.add(b, -w);
  }
  // [0, c)
  ll simple_sum(ll c){
    return P.sum(c) + Q.sum(c) * c;
  }
  // [a, b)
  ll sum(ll a, ll b){
    return simple_sum(b) - simple_sum(a);
  }
};

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

    // input
    ll N,D,A;
    cin >> N >> D >> A;

    debug("range", D);
    debug("damage", A);

    vector<PII> V;
    rep(i, N){
      ll x,h;cin>>x>>h;
      V.push_back(MP(x,h));
    }
    sort(ALL(V));

    auto range = Range(N+10);
    rep(i, N){
      ll x = V[i].first;
      ll h = V[i].second;
      range.update(i, i+1, h);
    }

    VI X(N);
    rep(i, N) X[i] = V[i].first;

    ll cnt=0;
    rep(i, N){

      ll rest_h = range.sum(i, i+1);
      debug(i, "H", rest_h);
      if(rest_h<=0){
        debug(i, "skip");
        continue;
      }

      ll n = (rest_h+A-1)/A; // 落とす回数
      cnt += n;
      debug(i, n);
      ll damage = A*n;


      // おとすところ
      ll bomb_x = V[i].first + D;

      // 右はじ
      ll bomb_r = bomb_x + D;
      auto it = lower_bound(ALL(X), bomb_r);
      if(it==X.end()){
        debug(i, "bomb to last");
        it--;
      }
      else if(*it==bomb_r){
        // ピッタリ
      }else{
        it--;
      }
      // itまでにダメージが入る
      ll idx = it - X.begin();
      range.update(0, idx+1, -damage);
    }

    p(cnt);
    return 0;
}

Measured memory_bytes: 8812