#include <bits/stdc++.h>
using namespace std;

// #include <boost/algorithm/string/join.hpp>
// using boost::algorithm::join;
//
// #include "boost/multi_array.hpp"
// boost::multi_array<int, 3> dp;
// dp.resize(boost::extents[10][9][8]);
//
// #include <boost/multiprecision/cpp_dec_float.hpp>  // quite slowly
// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision; // mp::log10
// using bigint = boost::multiprecision::cpp_int;
// using rational = mp::cpp_rational;  // double d = static_cast<double>(r);

typedef long long ll;
typedef unsigned long long ull;
//typedef long double ld;

typedef map<int, int> mii;
typedef pair<int, int> pii;
typedef pair<double,double> pdd;
typedef set<int> si;
typedef set<ll> sll;
typedef vector<int> vi;
typedef vector<pair<int, int > > vii;
typedef vector<ll> vll;
typedef vector<double> vd;
typedef vector<vi> vvi;
typedef vector<vii> vvii;
typedef vector<vll> vvll;

//constexpr ll MOD = 1e9+7;
template<typename T>constexpr auto inf=numeric_limits<T>::max()/4;
constexpr int INF=inf<int>;
constexpr ll LINF=inf<ll>;

#define Sort(x) sort(begin(x),end(x))
#define Reverse(x) reverse(begin(x),end(x))
#define ABS(a,b) ((a)<(b)?(b)-(a):(a)-(b))
#define nbit(n) (1ull<<(n))
#define _ol3(_1,_2,_3,name,...)name
#define _rep(i,n)_repi(i,0,n)
#define _repi(i,a,b)for(int i=a,i##_l=(b);i<i##_l;++i)
#define REP(...) _ol3(__VA_ARGS__,_repi,_rep,)(__VA_ARGS__)
#define REPR(i,n) for(int i=n-1;i>=0;--i)
#define REPA(i,v) REP(i,(v).size())

// sort(begin(x), end(x), greater<ll>());
// lower_bound(a.begin(), a.end(), val): a[i] ≥ valである最左の位置
// upper_bound(a.begin(), a.end(), val): a[i] > valである最左の位置

// Returns minimum of a and b.
// If a is less b, a is set to b.
template<typename T>
T chmin(T& a, T b) {
  if (a > b) {
    a = b;
  }
  return a;
}

// Returns maximum of a and b.
// If a is less b, a is set to b.
template<typename T>
T chmax(T& a, T b) {
  if (a < b) {
    a = b;
  }
  return a;
}

template <typename T>
void dumpContents(const T& v, const string& msg)
{
  cerr << "### " << msg << " ###\n";
  for (const auto& x : v) {
    cerr << x << " ";
  }
  cerr << endl;
}

struct before_main_function {
  before_main_function() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout<<setprecision(20)<<fixed;
#define endl "\n"
  }
} before_main_function;


// ========== end of template ==========

struct Monster {
  ll x, h;

  Monster(ll _x, ll _h)
    : x(_x), h(_h) { }

};

struct Damage {
  ll x, h;

  Damage(ll _x, ll _h)
    : x(_x), h(_h) { }

};

int main(int argc, char** argv) {
  int N;
  ll D, A;
  cin >> N >> D >> A;

  vector<Monster> monsters;
  REP(i, N) {
    ll x, h;
    cin >> x >> h;
    monsters.emplace_back(x, h);
  }

  sort(begin(monsters), end(monsters),
       [](const Monster& lhs, const Monster& rhs) {
         return lhs.x < rhs.x;
       });

  auto comp = [](const Damage& lhs, const Damage& rhs) {
         return lhs.x > rhs.x;
       };

  priority_queue<Damage, vector<Damage>, decltype(comp)> imos(comp);

  ll cur_damage = 0;
  ll cur_x = 0;
  ll ret = 0;
  REP(i, N) {
    Monster& monster = monsters[i];
    cur_x = monster.x;

    while (!imos.empty()) {
      const Damage damage = imos.top();
      if (damage.x > cur_x) break;

      cur_damage += damage.h;
      imos.pop();
    }

    assert(cur_damage>=0);

    monster.h -= cur_damage;
    if (monster.h<=0) continue;

    ll c = (monster.h+A-1)/A;
    ret += c;
    cur_damage += A*c;
    imos.push(Damage(cur_x+2*D+1, -A*c));
  }

  cout << ret << endl;


  return 0;
}

/* vim: set expandtab shiftwidth=2 softtabstop=2 : */


Measured memory_bytes: 7020