#include <bits/stdc++.h>
#define LLI long long int
#define FOR(v, a, b) for(LLI v = (a); v < (b); ++v)
#define FORE(v, a, b) for(LLI v = (a); v <= (b); ++v)
#define REP(v, n) FOR(v, 0, n)
#define REPE(v, n) FORE(v, 0, n)
#define REV(v, a, b) for(LLI v = (a); v >= (b); --v)
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define ITR(it, c) for(auto it = (c).begin(); it != (c).end(); ++it)
#define RITR(it, c) for(auto it = (c).rbegin(); it != (c).rend(); ++it)
#define EXIST(c,x) ((c).find(x) != (c).end())
#define fst first
#define snd second
#define popcount __builtin_popcount
#define UNIQ(v) (v).erase(unique(ALL(v)), (v).end())
#define bit(i) (1LL<<(i))

#ifdef DEBUG
#include <Mylib/Debug/debug.cpp>
#else
#define dump(...) ((void)0)
#endif

#define gcd __gcd

using namespace std;
template <class T> constexpr T lcm(T m, T n){return m/gcd(m,n)*n;}

template <typename I> void join(ostream &ost, I s, I t, string d=" "){for(auto i=s; i!=t; ++i){if(i!=s)ost<<d; ost<<*i;}ost<<endl;}
template <typename T> istream& operator>>(istream &is, vector<T> &v){for(auto &a : v) is >> a; return is;}
template <typename T> void puts_all(const T &value){std::cout << value << "\n";}
template <typename T, typename ...Args> void puts_all(const T &value, const Args&... args){std::cout << value << " ";puts_all(args...);}

template <typename T, typename U> bool chmin(T &a, const U &b){return (a>b ? a=b, true : false);}
template <typename T, typename U> bool chmax(T &a, const U &b){return (a<b ? a=b, true : false);}
template <typename T, size_t N, typename U> void fill_array(T (&a)[N], const U &v){fill((U*)a, (U*)(a+N), v);}
template <typename T> auto make_vector(int n, int m, const T &value){return vector<vector<T>>(n, vector<T>(m, value));}


struct Init{
  Init(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(12);
    cerr << fixed << setprecision(12);
  }
}init;


namespace sort_all{
  template <typename T>
  void sort_with_ord(const std::vector<int> &ord, int N, std::vector<T> &a){
    std::vector<T> temp(N);
    for(int i = 0; i < N; ++i) temp[i] = a[ord[i]];
    std::swap(temp, a);
  }

  template <typename T, typename ...Args>
  void sort_with_ord(const std::vector<int> &ord, int N, std::vector<T> &a, Args&... args){
    std::vector<T> temp(N);
    for(int i = 0; i < N; ++i) temp[i] = a[ord[i]];
    std::swap(temp, a);
    sort_with_ord(ord, N, args...);
  }

  template <typename Compare, typename ...Args>
  void run(const Compare &compare, int N, Args&... args){
    std::vector<int> ord(N);
    std::iota(ord.begin(), ord.end(), 0);
    std::sort(ord.begin(), ord.end(), compare);

    sort_with_ord(ord, N, args...);
  }
};


template <typename T, typename Func>
class DualSegmentTree{
private:
  const int depth, size, hsize;
  const T e;
  const Func f;
  std::vector<T> data;
  
  inline void propagate(int i){
    if(i < hsize){
      data[i << 1 | 0] = f(data[i], data[i << 1 | 0]);
      data[i << 1 | 1] = f(data[i], data[i << 1 | 1]);
      data[i] = e;
    }
  }

  inline void propagate_top_down(int i){
    std::vector<int> temp;
    while(i > 1){
      i >>= 1;
      temp.push_back(i);
    }

    for(auto it = temp.rbegin(); it != temp.rend(); ++it){
      propagate(*it);
    }
  }
  
public:
  DualSegmentTree(int n, const T &e, const Func &f):
    depth(n > 1 ? 32-__builtin_clz(n-1) + 1 : 1),
    size((1 << depth) - 1),
    hsize(size / 2 + 1),
    e(e),
    f(f),
    data(size + 1, e)
  {}

  inline void update(int l, int r, const T &x){
    propagate_top_down(l + hsize);
    propagate_top_down(r + hsize);

    int L = l + hsize;
    int R = r + hsize;
    
    while(L < R){
      if(R & 1){
        --R;
        data[R] = f(x, data[R]);
      }
      if(L & 1){
        data[L] = f(x, data[L]);
        ++L;
      }

      L >>= 1;
      R >>= 1;
    }
  }

  inline T get(int i){
    propagate_top_down(i + hsize);
    return data[i + hsize];
  }

  void init_with_vector(const std::vector<T> &a){
    data.assign(size + 1, e);
    for(int i = 0; i < (int)a.size(); ++i) data[hsize + i] = a[i];
  }
  
  void debug(){
#ifdef DEBUG
    std::cerr << "{";
    for(int i = 0; i < hsize; ++i){
      if(i) std::cerr << ",";
      std::cerr << get(i);
    }
    std::cerr << "}" << std::endl;
#endif
  }
};


template <typename T>
auto make_dual_segment_tree_range_add(int size, const T &e){
  return DualSegmentTree<T, std::plus<T>>(size, e, std::plus<T>());
}



int main(){
  LLI N, D, A;
  while(cin >> N >> D >> A){
    vector<LLI> X(N), H(N);
    REP(i,N) cin >> X[i] >> H[i];

    sort_all::run([&](int i, int j){return X[i] < X[j];}, N, X, H);

    auto seg = make_dual_segment_tree_range_add<LLI>(N, 0);
    seg.init_with_vector(H);
    
    LLI ans = 0;

    REP(i,N){
      if(seg.get(i) <= 0) continue;

      int k = upper_bound(ALL(X), X[i] + 2 * D) - X.begin();

      LLI t = (seg.get(i) + A - 1) / A;
      ans += t;

      seg.update(i, k, - t * A);
    }

    cout << ans << endl;
  }

  return 0;
}


Measured memory_bytes: 7480