#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
#define rep(i, n) for(ll i = 0;i < n;i++)
#define all(i) i.begin(), i.end()
template<class T, class U> bool cmax(T& a, U b) { if (a<b) {a = b; return true;} else return false; }
template<class T, class U> bool cmin(T& a, U b) { if (a>b) {a = b; return true;} else return false; }

//http://judge.u-aizu.ac.jp/onlinejudge/review.jsp?rid=2642766#1
// Abstract Lazy Segment Tree (????±?????±?????????¶?????°???????????¨)
const ll SIZE = 400020;
template<typename T>
struct lazysegtree {
    // ?????????????????????
    T node[2*SIZE], lazy[2*SIZE], I;
    bool need_upd[2*SIZE];

    // ????????¬????????§??? (update, query ??? 2 ???????????????)
    // update function ??????????????????????????¢????????????
    // upd_f(X, Y, l, r) -> ????????? [l, r) ??§???????????????????????? X ??? Y ????????????
    // lazy ???????????? update ??¨??????????????? 1 ??????????????¨?????°?????????
    T (*upd_f)(T, T, ll, ll), (*qry_f)(T, T);

    // ???????????¨?????????????????????????????¨?????? node ??¨ lazy ??????????????§?????????
    lazysegtree(T (*op1)(T, T, ll, ll), T (*op2)(T, T), T X) {
        upd_f = op1;
        qry_f = op2;
        I = X;
        fill(lazy, lazy+2*SIZE, I);
        fill(node, node+2*SIZE, I);
        fill(need_upd, need_upd+2*SIZE, false);
    }

    void lazy_eval(ll k, ll l, ll r) {
        if(!need_upd[k]) return;
        node[k] = upd_f(node[k], lazy[k], l, r);
        if(r - l > 1) {
            lazy[2*k+1] = upd_f(lazy[2*k+1], lazy[k], 0, 1);
            lazy[2*k+2] = upd_f(lazy[2*k+2], lazy[k], 0, 1);
            need_upd[2*k+1] = need_upd[2*k+2] = true;
        }
        lazy[k] = I;
        need_upd[k] = false;
    }

    // ???????????? [a, b) ??????????????? val ??????????????????
    // (upd_f ?????¨????????????)
    void update(ll a, ll b, T val, ll l=0, ll r=SIZE, ll k=0) {
        lazy_eval(k, l, r);
        if(b <= l || r <= a) return;
        if(a <= l && r <= b) {
            lazy[k] = upd_f(lazy[k], val, 0, 1);
            need_upd[k] = true;
            lazy_eval(k, l, r);
        }
        else {
            ll mid = (l + r) / 2;
            update(a, b, val, l, mid, 2*k+1);
            update(a, b, val, mid, r, 2*k+2);
            node[k] = qry_f(node[2*k+1], node[2*k+2]);
        }
    }

    // ???????????? [a, b) ?????????????????¨???????????????
    // (qry_f ?????¨????????????)
    T query(ll a, ll b, ll l=0, ll r=SIZE, ll k=0) {
        lazy_eval(k, l, r);
        if(b <= l || r <= a) return I;
        if(a <= l && r <= b) return node[k];
        ll mid = (l + r) / 2;
        T vl = query(a, b, l, mid, 2*k+1);
        T vr = query(a, b, mid, r, 2*k+2);
        return qry_f(vl, vr);
    }
};

// [[???????????????]]
// update ??¨??¨ query ??¨?????¢??°??¨????????? (??¢??°????????????????????????????????????????????????) ?????¨???????????£?¨???????
// ??????????????¨???update ??¨?????¢??°??? upd ??§???query ??¨?????¢??°??? fnd ??§??????????????? INT_MAX

ll upd(ll a, ll b, ll l, ll r) {return a + (r - l) * b;}
ll fnd(ll a, ll b) {return a + b;}
lazysegtree<ll> seg(upd, fnd, 0);

ll f(ll a, ll b) {
  if (a%b == 0) {
    return a/b;
  } else {
    return a/b+1;
  }
}

int main() {
  cin.tie(0); ios::sync_with_stdio(false);

  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));

  ll ans = 0;
  rep(i, n) {
    if (seg.query(i, i+1) < v[i].second) {
      ll t = f(v[i].second-seg.query(i, i+1), a);
      ans += t;
      ll c = upper_bound(all(v), pll(v[i].first+2*d, 1LL<<60))-v.begin()-i;
      seg.update(i, i+c, t*a);
    }
  }
  cout << ans << endl;
}


Measured memory_bytes: 16640