#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <set>
#include <map>
#include <queue>
#include<limits.h>
#include<iomanip>
#include <cassert>
#define rep(i, n) for(int i = 0; i < n; i++)
#define rrep(i, n) for(int i = n-1; i >= 0; i--)
#define REP(i, m, n) for(int i = m; i < n; i++)
#define ALL(v) v.begin(),v.end()
#define RALL(v) v.rbegin(),v.rend()
#define Cout(x) cout << x << endl;
#define check(v) rep(i,v.size()) cout << v[i] << endl;
#define vint(x) vector<int> x
#define vll(x) vector<long long> x
#define vstr(x) vector<string> x
const long long LLINF = 1LL<<60;
const int INF = 1e9;
const long long MOD = 1000000007;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
typedef long long ll;
#define pint pair<int,int>
#define pll pair<ll,ll>
using namespace std;
//オーバーフローに気をつけろよおおおおおお
//確認忘れるなよおおおおおお

struct LazySegmentTree {
private:
public:
    int n;
    vector<ll> node, lazy;
 
    LazySegmentTree(vector<ll> v) {
        int sz = (int)v.size();
        n = 1;
        while (n < sz)
            n *= 2;
        node.resize(2 * n - 1);
        lazy.resize(2 * n - 1, 0);
 
        for (int i = 0; i < sz; i++)
            node[i + n - 1] = v[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[2 * k + 1] += lazy[k] / 2;
                lazy[2 * k + 2] += lazy[k] / 2;
            }
            lazy[k] = 0;
        }
    }
 
    void add(int a, int b, ll x, int k = 0, int l = 0, int r = -1) {
        if (r < 0)
            r = n;
        eval(k, l, r);
        if (b <= l || r <= a)
            return;
        if (a <= l && r <= b) {
            lazy[k] += (r - l) * x;
            eval(k, l, r);
        } else {
            add(a, b, x, 2 * k + 1, l, (l + r) / 2);
            add(a, b, x, 2 * k + 2, (l + r) / 2, r);
            node[k] = node[2 * k + 1] + node[2 * k + 2];
        }
    }
 
    ll getsum(int a, int b, int k = 0, int l = 0, int r = -1) {
        if (r < 0)
            r = n;
        eval(k, l, r);
        if (b <= l || r <= a)
            return 0;
        if (a <= l && r <= b)
            return node[k];
        ll vl = getsum(a, b, 2 * k + 1, l, (l + r) / 2);
        ll vr = getsum(a, b, 2 * k + 2, (l + r) / 2, r);
        return vl + vr;
    }
};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    ll n, d, a; cin >> n >> d >> a;
    vector<pll> v(n);
    rep(i,n) cin >> v[i].first >> v[i].second;
    vector<ll> x(n), h(n);
    sort(ALL(v));
    rep(i,n) {
        x[i] = v[i].first;
        h[i] = v[i].second;
    }
    ll ans = 0;
    LazySegmentTree seg(h);
    rep(i,n) {
        int hp = seg.getsum(i,i+1);
        if(hp<=0) continue;
        auto iter = upper_bound(ALL(x), x[i]+2*d);
        int index = iter-x.begin();
        int time = (hp-1)/a + 1;
        seg.add(i,index, -a * time);
        ans += time;
    }
    cout << ans << endl;

    return 0;
}

Measured memory_bytes: 16256