//#include <bits/stdc++.h>

#include <iostream>
#include <algorithm>

#include <bitset>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>
#include <cstring>
#include <string>
#include <utility>
#include <array>
#include <complex>
#include <valarray>

#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>

#include<memory>


using namespace std;
#define int long long

typedef long long ll;
typedef unsigned long long ull;
//typedef unsigned __int128 HASH;
typedef pair<int,int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll,int> plli;
typedef pair<double,int> pdi;
typedef pair<long double, int> pdbi;
typedef pair<int,pii> pipii;
typedef pair<ll,pll> plpll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;
typedef vector<vector<int>> mat;

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n);i>0;i--)
#define rrep2(i,a,b) for (int i=(a);i>b;i--)
#define fi first
#define se second
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()

template <class T>
using MINPQ = std::priority_queue<T, vector<T>, greater<T>>; //MINPQ<pii> pq;
template <class T>
using MAXPQ = std::priority_queue<T>;


const ll hmod1 = 999999937;
const ll hmod2 = 1000000000 + 9;
const int INF = 1<<30;
const ll INFLL = 1LL<<62;
const double EPS = 1e-12;
const ll mod = 1000000000 + 7;
//const ll mod = 998244353;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const long double pi = 3.141592653589793;

#define addm(X, Y) (X) = ((X) + ((Y) % mod) + mod) % mod
#define inside(y, x, h, w) (0 <= (y) && (y) < (h) && 0 <= (x) && (x) < (w)) ? true : false
#define stand(B, i) (((B>>i) & 1) == 1) ? true : false //Bのi番目のbitが1ならtrue, 0ならfalse

//debug
#define DEBUG

#define DUMPOUT cerr

#ifdef DEBUG
#define dump(...) DUMPOUT<<#__VA_ARGS__<<" :["<<__FUNCTION__<<":"<<__LINE__<<"]"<<endl; DUMPOUT<<"    "; dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

void dump_func() {DUMPOUT << endl;};

template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) == 0) DUMPOUT << " ";
    else DUMPOUT << ", ";
    dump_func(std::move(tail)...);
}

//ostream
template<typename T> ostream& operator << (ostream& os, vector<T>& vec) {
    os << "["; for (int i = 0; i<vec.size(); i++) os << vec[i] << (i + 1 == vec.size() ? "" : ", "); os << "]";
    return os;
}

template<typename T, typename U> ostream& operator << (ostream& os, pair<T, U>& pair_var) {
    os << "(" << pair_var.first << ", " << pair_var.second << ")";
    return os;
}

template<typename T, typename U> ostream& operator << (ostream& os, map<T, U>& map_var) {
    os << "[";
    for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
        os << "(" << itr->first << ", " << itr->second << ")"; itr++;  if(itr != map_var.end()) os << ", "; itr--;
    }
    os << "]";
    return os;
}

template<typename T> ostream& operator << (ostream& os, set<T>& set_var) {
    os << "[";
    for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
        os << *itr; ++itr; if(itr != set_var.end()) os << ", "; itr--;
    }
    os << "]";
    return os;
}

int n, d, a;
vector<int> x;
vector<pii> xh;

struct StarrySkyTree {
    int size;
    vector<int> node, lazy;

    StarrySkyTree (int n) {
        size = 1;
        while (size < n) size *= 2;
        node.resize(2 * size - 1, 0);
        lazy.resize(2 * size - 1, 0);
    }

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

    void add(int L, int R, int x, int k, int nodeL, int nodeR) {
        eval(nodeL, nodeR, k);
        if (nodeR <= L || R <= nodeL) return;
        if (L <= nodeL && nodeR <= R) {
            lazy[k] += x;
            eval(nodeL, nodeR, k);
            return;
        }
        int nodeM = (nodeL + nodeR) / 2;
        add(L, R, x, 2 * k + 1, nodeL, nodeM);
        add(L, R, x, 2 * k + 2, nodeM, nodeR);
        node[k] = min(node[2 * k + 1], node[2 * k + 2]);
    }
    void add(int L, int R, int x) {
        add(L, R, x, 0, 0, size);
    }

    int get(int queryL, int queryR, int k, int nodeL, int nodeR) {
        eval(nodeL, nodeR, k);
        if (nodeR <= queryL || queryR <= nodeL) return INFLL;
        if (queryL <= nodeL && nodeR <= queryR) {
            return node[k];
        }
        int nodeM = (nodeL + nodeR) / 2;
        int vl = get(queryL, queryR, 2 * k + 1, nodeL, nodeM);
        int vr = get(queryL, queryR, 2 * k + 2, nodeM, nodeR);
        return min(vl, vr);
    }
    int get(int queryL, int queryR) {
        return get(queryL, queryR, 0, 0, size);
    }
};

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> d >> a;
  x.resize(n);
  rep(i, n) {
    int h;
    cin >> x[i] >> h;
    xh.push_back({x[i], h});
  }
  sort(all(x));
  sort(all(xh));
  int ans = 0;
  StarrySkyTree seg(n);
  rep(i, n) {
    seg.add(i, i+1, xh[i].se);
  }
  rep(i, n) {
    int now_h = seg.get(i, i+1);
    if (now_h <= 0) continue;
    int now_x = xh[i].fi;
    int idx = upper_bound(all(x), now_x + 2*d) - x.begin();
    int cnt = (now_h + a-1) / a;
    ans += cnt;
    seg.add(i, idx, -a*cnt);
  }
  cout << ans << endl;
}


Measured memory_bytes: 14060