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

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define bit(n) (1LL<<(n))
// functions
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(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << p.first << " " << p.second; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(0); cout << fixed << setprecision(20);}
} fast_io_;

template<typename T, typename E>
struct LazySegmentTree_ {
  function<T(T, T)> f; // aggregation
  function<E(E, E)> h; // update lazy element
  function<T(T, E, int)> p; // update element with lazy element
  int n;
  T def;
  E l_def;
  vector<T> vec;
  vector<E> lazy;
  LazySegmentTree_(){}
  LazySegmentTree_(int n_, function<T(T, T)> f, T def,
      function<E(E, E)> h, E l_def, function<T(T, E, int)> p,
                   vector<T> v=vector<T>()): f(f), def(def), h(h), l_def(l_def), p(p){

    // initialize vector
    n = 1;
    while(n < n_){
      n *= 2;
    }
    vec = vector<T>(2*n-1, def);
    lazy = vector<E>(2*n-1, l_def);

    // initialize segment tree
    for(int i = 0; i < v.size(); i++){
      vec[i + n - 1] = v[i];
    }
    for(int i = n - 2; i >= 0; i--){
      vec[i] = f(vec[2*i+1], vec[2*i+2]);
    }
  }
  void eval(int k, int len){
    if(lazy[k] != l_def){
      if(k < n - 1){
        lazy[2*k+1] = h(lazy[2*k+1], lazy[k]);
        lazy[2*k+2] = h(lazy[2*k+2], lazy[k]);
      }
      vec[k] = p(vec[k], lazy[k], len);
      lazy[k] = l_def;
    }
  }
  T update(int a, int b, const E &val, int k, int l, int r){
    eval(k, r - l);
    if(r <= a || b <= l){
      return vec[k];
    }else if(a <= l && r <= b){
      lazy[k] = h(lazy[k], val);
      eval(k, r - l);
      return vec[k];
    }else{
      return vec[k] = f(update(a, b, val, 2*k+1, l, (l+r)/2),
          update(a, b, val, 2*k+2, (l+r)/2, r));
    }
  }
  T update(int a, int b, E val){
    return update(a, b, val, 0, 0, n);
  }
  // [l, r) -> [a, b) (at k)
  T query(int a, int b, int k, int l, int r){
    eval(k, r - l);
    if(r <= a || b <= l)return def;
    if(a <= l && r <= b)return vec[k];
    T ld = query(a, b, 2*k+1, l, (l+r)/2);
    T rd = query(a, b, 2*k+2, (l+r)/2, r);
    return f(ld, rd);
  }
  T query(int a, int b){
    return query(a, b, 0, 0, n);
  }
};

template<typename T, typename E>
using LazySegmentTree = struct LazySegmentTree_<T, E>;
using LazySegmentTreeI = LazySegmentTree<int, int>;
using LazySegmentTreeL = LazySegmentTree<long long, long long>;


int main(int argc, char const* argv[])
{
  int n; cin >> n;
  ll d, a; cin >> d >> a;
  vector<ll> x(n), h(n); rep(i, n)cin >> x[i] >> h[i];
  vector<int> e(n); rep(i, n)e[i] = i;
  sort(whole(e), [&](int i, int j){
    return x[i] < x[j];
  });
  vector<ll> vi(n, 0); rep(i, n)vi[i] = h[e[i]];
  vector<ll> xi(n, 0); rep(i, n)xi[i] = x[e[i]];
  LazySegmentTreeL seg = LazySegmentTreeL(n, [](ll a, ll b){return a + b;},
                                          0, [](ll a, ll b){return a + b;},
                                          0, [](ll a, ll b, int c){return a + b * c;},
                                          vi);
  
  
  ll res = 0;
  rep(i, n){
    int I = e[i];
    int H = seg.query(i, i + 1);
    if(H <= 0)continue;
    int idx = upper_bound(whole(xi), x[I] + 2 * d) - xi.begin();
    ll tmp = (H + a - 1) / a;
    res += tmp;
    seg.update(i, idx, - tmp * a);
  }
  cout << res << endl;
  return 0;
}


Measured memory_bytes: 17024