#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> P;
typedef pair<int,int> Pi;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define FOR(i, a, b) for (ll i = a; i < b; i++)
#define fi first
#define se second
#define endl "\n"

template<typename T> inline bool chmax(T &a, T b){if(a<b){a=b;return true;}return false;}
template<typename T> inline bool chmin(T &a, T b){if(a>b){a=b;return true;}return false;}
template<typename T> ostream& operator<<(ostream& s,const complex<T>& d) {return s<<"("<<d.real()<<", "<<d.imag()<< ")";}
template<typename T1, typename T2> ostream& operator<<(ostream& s,const pair<T1,T2>& d) {return s<<"("<<d.first<<", "<<d.second<<")";}
template<typename T> ostream& operator<<(ostream& s, const vector<T>& d){
	int len=d.size();
	rep(i,len){
		s<<d[i];if(i<len-1) s<<" ";
	}
	return s;
}
template<typename T> ostream& operator<<(ostream& s,const vector<vector<T>>& d){
	int len=d.size();
	rep(i,len){
		s<<d[i]<<endl;
	}
	return s;
}
template<typename T> ostream& operator<<(ostream& s,const set<T>& v){
	s<<"{ ";
	for(auto itr=v.begin();itr!=v.end();++itr) {
		if (itr!=v.begin()) {s<< ", ";}
		s<<(*itr);
	}
	s<<" }";
	return s;
}
template<typename T1, typename T2> ostream& operator<<(ostream& s,const map<T1,T2>& m){
	s<<"{"<<endl;
	for(auto itr=m.begin();itr!=m.end();++itr){
		s<<" "<<(*itr).first<<" : "<<(*itr).second<<endl;
	}
	s<<"}"<<endl;
	return s;
}

const ll mod=1e9+7;
const ll inf=1e17;
const int INF=1e9;
const double PI=acos(-1);
const double EPS=1e-10;

//区間加算と区間和
/*
verified by
http://judge.u-aizu.ac.jp/onlinejudge/review.jsp?rid=3982700#1
*/
struct LazySegmentTree{
private:
    int n;
    vector<ll> node,lazy;
    vector<bool> lazyFlag;
 
public:
    LazySegmentTree(){
        int sz=200050;
        n=1;
		while(n < sz) n*=2;
        node.resize(2*n-1,0);
        lazy.resize(2*n-1,0);
        lazyFlag.resize(2*n-1,false);
    }
    void lazyEvaluate(int k,int l,int r){
        if(lazyFlag[k]){
            node[k]+=lazy[k];
            if(r-l>1) {
                lazy[k*2+1]+=lazy[k]/2;
                lazy[k*2+2]+=lazy[k]/2;
                lazyFlag[k*2+1]=lazyFlag[k*2+2]=true;
            }
            lazyFlag[k]=false;
            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;
        lazyEvaluate(k,l,r);
        if(b<=l || r<=a) return ;
        if(a<=l && r<=b) {
            lazy[k]+=x*(r-l);
            lazyFlag[k]=true;
            lazyEvaluate(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;
        lazyEvaluate(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(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	ll n,d,a;
	cin>>n>>d>>a;
	vector<P> g(n);
	rep(i,n){
		cin>>g[i].fi>>g[i].se;
	}
	sort(begin(g),end(g));
	vector<ll> x(n),h(n);
	LazySegmentTree seg;
	rep(i,n){
		x[i]=g[i].fi;
		h[i]=g[i].se;
		seg.add(i,i+1,h[i]);
	}
	ll ans=0;
	rep(i,n){
		ll nowh=seg.getsum(i,i+1);
		if(nowh<0) continue;
		ll now=x[i];
		ll ind=lower_bound(begin(x),end(x),now+2*d)-begin(x);
		if(ind==n || x[ind]-now>2*d) ind--;
		ll cnt=(nowh+a-1)/a;//必要な攻撃回数
		//cout<<nowh<<' '<<cnt<<endl;
		seg.add(i,ind+1,-cnt*a);
		ans+=cnt;
	}
	cout<<ans<<endl;
}

Measured memory_bytes: 14720