/*
confirm 0LL and 1LL
confirm cornercases such as 0
confirm times of cin < 10^6
*/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<ll, ll>;
using Pld = pair<ld, ld>;
using Vec = vector<ll>;
using VecP = vector<P>;
using VecB = vector<bool>;
using VecC = vector<char>;
using VecD = vector<ld>;
using VecS = vector<string>;
using VecVec = vector<Vec>;
using Graph = vector<VecP>;
template <typename T>
using Vec1 = vector<T>;
template <typename T>
using Vec2 = vector<Vec1<T> >;
#define REP(i, m, n) for(ll (i) = (m); (i) < (n); ++(i))
#define REPN(i, m, n) for(ll (i) = (m); (i) <= (n); ++(i))
#define REPR(i, m, n) for(ll (i) = (m)-1; (i) >= (n); --(i))
#define REPNR(i, m, n) for(ll (i) = (m); (i) >= (n); --(i))
#define rep(i, n) REP(i, 0, n)
#define repn(i, n) REPN(i, 1, n)
#define repr(i, n) REPR(i, n, 0)
#define repnr(i, n) REPNR(i, n, 1)
#define all(s) (s).begin(), (s).end()
#define pb push_back
#define mp make_pair
#define fs first
#define sc second
template <typename T>
bool chmax(T &a, const T& b){if(a < b){a = b; return true;} return false;}
template <typename T>
bool chmin(T &a, const T& b){if(a > b){a = b; return true;} return false;}
template <typename T>
void co(const T n){cout << n << endl;}
template <typename T>
void cosp(const T n){cout << n << ' ';}
template <typename T>
void coVec(const Vec1<T> &v){for(T i : v) cosp(i); cout << endl;}
void sonic(){ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);}
void setp(const ll n){cout << fixed << setprecision(n);}
const ll INF = 1e9+1;
const ll LINF = 1e18+1;
const ll MOD = 1e9+7;
//const ll MOD = 998244353;
const ld PI = acos(-1);
const ld EPS = 1e-11;

template <typename T,typename E>
struct SegmentTree{
  typedef function<T(T,T)> F;
  typedef function<T(T,E)> G;
  typedef function<E(E,E)> H;
  typedef function<E(E,int)> P;
  int n;
  F f;
  G g;
  H h;
  P p;
  T d1;
  E d0;
  vector<T> dat;
  vector<E> laz;
  SegmentTree(int n_,F f,G g,H h,T d1,E d0,
	      vector<T> v=vector<T>(),P p=[](E a,int b){return a;}):
    f(f),g(g),h(h),d1(d1),d0(d0),p(p){
    init(n_);
    if(n_==(int)v.size()) build(n_,v);
  }
  void init(int n_){
    n=1;
    while(n<n_) n*=2;
    dat.clear();
    dat.resize(2*n-1,d1);
    laz.clear();
    laz.resize(2*n-1,d0);
  }
  void build(int n_, vector<T> v){
    for(int i=0;i<n_;i++) dat[i+n-1]=v[i];
    for(int i=n-2;i>=0;i--)
      dat[i]=f(dat[i*2+1],dat[i*2+2]);
  }
  inline void eval(int len,int k){
    if(laz[k]==d0) return;
    if(k*2+1<n*2-1){
      laz[k*2+1]=h(laz[k*2+1],laz[k]);
      laz[k*2+2]=h(laz[k*2+2],laz[k]);
    }
    dat[k]=g(dat[k],p(laz[k],len));
    laz[k]=d0;
  }
  T update(int a,int b,E x,int k,int l,int r){
    eval(r-l,k);
    if(r<=a||b<=l) return dat[k];
    if(a<=l&&r<=b){
      laz[k]=h(laz[k],x);
      return g(dat[k],p(laz[k],r-l));
    }
    return dat[k]=f(update(a,b,x,k*2+1,l,(l+r)/2),
		    update(a,b,x,k*2+2,(l+r)/2,r));
  }
  T update(int a,int b,E x){
    return update(a,b,x,0,0,n);
  }
  T query(int a,int b,int k,int l,int r){
    eval(r-l,k);
    if(r<=a||b<=l) return d1;
    if(a<=l&&r<=b) return dat[k];
    T vl=query(a,b,k*2+1,l,(l+r)/2);
    T vr=query(a,b,k*2+2,(l+r)/2,r);
    return f(vl,vr);
  }
  T query(int a,int b){
    return query(a,b,0,0,n);
  }
};

int main(void){
	ll n, d, a;
	cin >> n >> d >> a;
	VecP p(n);
	rep(i, n) cin >> p[i].fs >> p[i].sc;
	sort(all(p));
	Vec x(n), h(n);
	rep(i, n){
		x[i] = p[i].fs;
		h[i] = p[i].sc;
	}

	SegmentTree<ll, ll> st((int)n, plus<ll>(), plus<ll>(), plus<ll>(), 0, 0, vector<ll>(n,0), multiplies<ll>());

	st.build(n, h);

	ll ans = 0;
	rep(i, n){
		ll b = st.query(i, i+1);
		if(b <= 0) continue;
		ll cnt = b/a;
		if(b%a) cnt++;
		ans += cnt;
		ll pos = upper_bound(all(x), x[i]+2*d)-x.begin();
		st.update(i, pos, -cnt*a);
	}
	co(ans);

	return 0;
}


Measured memory_bytes: 17792