#include <bits/stdc++.h>
using namespace std;
struct edge {
    int to;     // 辺の行き先
    int weight; // 辺の重み
    edge(int t, int w) : to(t), weight(w) { }
};
using Graph = vector<vector<int>>;
using dou =long double;
string Yes="Yes";
string YES="YES";
string NO="NO";
string No="No";
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; }
#define rep(i, n)         for(int i = 0; i < (int)(n); i++)
#define brep(n)           for(int bit=0;bit<(1<<n);bit++)
#define erep(i,container) for (auto i : container)
#define irep(i, n)        for(int i = n-1; i >= (int)0; i--)
#define rrep(i,m,n) for(int i = m; i < (int)(n); i++)
#define reprep(i,j,h,w) rep(i,h)rep(j,w)
#define all(x) (x).begin(),(x).end()
#define aall(x,n) (x).begin(),(x).begin()+(n)
#define VEC(type,name,n) std::vector<type> name(n);rep(i,n)std::cin >> name[i];
#define pb push_back
#define pf push_front
#define lb lower_bound
#define ub upper_bound
#define res resize
#define as assign
#define fi first
#define se second
#define itn int
#define mp make_pair
#define sum(a) accumulate(all(a),0ll)
#define keta fixed<<setprecision
#define vvector(name,typ,m,n,a)vector<vector<typ> > name(m,vector<typ> (n,a))
#define vvvector(name,t,l,m,n,a) vector<vector<vector<t> > > name(l, vector<vector<t> >(m, vector<t>(n,a)));
#define vvvvector(name,t,k,l,m,n,a) vector<vector<vector<vector<t> > > > name(k,vector<vector<vector<t> > >(l, vector<vector<t> >(m, vector<t>(n,a)) ));
 
typedef long long ll;
//typedef long long T;
const int INF = 2000000000;
const ll INF64 = 922337203685477580ll;
const int mod = 1000000007ll;
const ll  MOD = 1000000007LL;

//int N, Q;
struct LazySegmentTree {
private:
    int n;
    vector<ll> node, lazy;
 
public:
    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(){
    int n;
    ll d,a;
    std::cin >> n>>d>>a;
    std::vector<ll> x(n),h(n),p(n);
    rep(i,n){
        std::cin >> x[i]>>h[i];
    }
    std::vector<pair<ll,ll>>pai(n) ;
    rep(i,n){
        pai[i].fi=x[i];
        pai[i].se=h[i];
    }
    sort(all(pai));
    rep(i,n){
        x[i]=pai[i].fi;
        h[i]=pai[i].se;
    }
    LazySegmentTree s(std::vector<ll>(n,0));
    rep(i,n){
        s.add(i,i+1,h[i]);
    }
    ll ans=0;
    rep(i,n){
        p[i]=int(ub(all(x),x[i]+2*d)-x.begin());
      //  std::cout << x[i] << std::endl;
    //    std::cout <<x[i]+2*d<<" "<< p[i] << std::endl;
    }
    rep(i,n){
        if(s.getsum(i,i+1)>0){
            ll cnt=ceil(double(s.getsum(i,i+1))/a);
            ll da=cnt*a;
            s.add(i,p[i],-da);
            ans+=cnt;
        }
    }
    std::cout << ans << std::endl;
    
}

Measured memory_bytes: 17792