#include <bits/stdc++.h>
using namespace std;
//#include <boost/multiprecision/cpp_int.hpp>
//using multiInt = boost::multiprecision::cpp_int;

using ll = long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
template <typename Q_temp>
using smaller_queue = priority_queue<Q_temp, vector<Q_temp>, greater<Q_temp>>;

const ll MOD = (ll)(1e9 + 7);
const int INF = (int)1e9;
const ll LINF = (ll)4e18;
const double PI = acos(-1.0);

#define REP(i, m, n) for (ll i = m; i < (ll)(n); ++i)
#define rep(i, n) REP(i, 0, n)
#define MP make_pair
#define MT make_tuple
#define YES(n) cout << ((n) ? "YES" : "NO") << endl
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl
#define Possible(n) cout << ((n) ? "Possible" : "Impossible") << endl
#define possible(n) cout << ((n) ? "possible" : "impossible") << endl
#define Yay(n) cout << ((n) ? "Yay!" : ":(") << endl
#define all(v) v.begin(), v.end()
#define NP(v) next_permutation(all(v))
#define dbg(x) cerr << #x << ":" << x << endl;

vector<int> Dx = {0, 0, -1, 1, -1, 1, -1, 1, 0};
vector<int> Dy = {1, -1, 0, 0, -1, -1, 1, 1, 0};

template <typename T>
struct LazySegmentTree
{

private:
  int n;
  T init_v;
  vector<T> node;
  vector<T> lazy;

public:
  LazySegmentTree(vector<T> a, T _init_v)
  {

    n = 1;
    init_v = _init_v;

    int sz = a.size();
    while (n < sz)
      n *= 2;

    node.resize(2 * n, init_v);
    lazy.resize(2 * n, init_v);

    for (int i = 0; i < sz; i++)
      node[i + n - 1] = a[i];
    for (int i = n - 2; i >= 0; i--)
      node[i] = node[i * 2 + 1] + node[i * 2 + 2];
  }

  void eval(int k, int l, int r)
  {
    if (lazy[k] != 0)
    {
      node[k] += lazy[k];
      if (r - l > 1)
      {
        lazy[k * 2 + 1] += lazy[k] / 2;
        lazy[k * 2 + 2] += lazy[k] / 2;
      }
      lazy[k] = 0;
    }
  }

  void add(int a, int b, T x, int k = 0, int l = 0, int r = -1)
  {
    if (r < 0)
      r = n;
    eval(k, l, r);
    if (r <= a || b <= l)
      return;
    if (a <= l && r <= b)
    {
      lazy[k] += (r - l) * x;
      eval(k, l, r);
    }
    else
    {
      add(a, b, x, k * 2 + 1, l, (l + r) / 2);
      add(a, b, x, k * 2 + 2, (l + r) / 2, r);
      node[k] = node[k * 2 + 1] + node[k * 2 + 2];
    }
  }

  T getsum(int a, int b, int k = 0, int l = 0, int r = -1)
  {
    if (r < 0)
      r = n;
    eval(k, l, r);
    if (r <= a || b <= l)
      return 0;
    if (a <= l && r <= b)
      return node[k];
    T lv = getsum(a, b, k * 2 + 1, l, (l + r) / 2);
    T rv = getsum(a, b, k * 2 + 2, (l + r) / 2, r);
    return lv + rv;
  }
};

inline ll CEIL(ll a, ll b)
{
  return (a + b - 1) / b;
}

int main()
{
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << setprecision(20) << setiosflags(ios::fixed);
  ll n, d, a;
  cin >> n >> d >> a;
  vector<pll> v(n);
  rep(i, n) cin >> v[i].first >> v[i].second;
  sort(all(v));
  vector<ll> v2(n);
  rep(i, n) v2[i] = v[i].second;

  LazySegmentTree<ll> sg(v2, 0LL);

  ll sum = 0;
  rep(i, n)
  {
    ll cnt = CEIL(sg.getsum(i, i + 1), a);
    if (cnt <= 0)
      continue;
    sum += cnt;
    auto itr = upper_bound(all(v), MP(v[i].first + 2 * d, LINF));
    ll r = distance(v.begin(), itr);
    sg.add(i, r, -cnt * a);
  }
  cout << sum << endl;

  return 0;
}


Measured memory_bytes: 14720