#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
inline ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b)*b; }
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T>& V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> >& Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T>& mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }
template<typename T>vector<T> make_v(size_t a){return vector<T>(a);}
template<typename T,typename... Ts>auto make_v(size_t a,Ts... ts){return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}
template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}

/*
 1-index
 RangeAdd : [s,t] に xを加算
 RangeSum : [s,t] の総和を出力
 */
struct BIT {
    int N;
    vector<ll> bit1;
    vector<ll> bit2;
    BIT(ll N):N(N) {
        /* BITは[1..N]で扱う */
        bit1.resize(N + 1, 0);
        bit2.resize(N + 1, 0);
    }
    
    void add1(int x, ll val){
        while (x <= N) {
            bit1[x] += val;
            x += x & -x;
        }
    }
    void add2(int x, ll val){
        while (x <= N) {
            bit2[x] += val;
            x += x & -x;
        }
    }
    
    // [l,r]
    void RangeAdd(int l,int r,ll val){
        // Update BIT1
        add1(l,val);
        add1(r+1,-val);
        
        // Update BIT2
        add2(l,val*(l-1));
        add2(r+1,-val*r);
    }
    
    ll sum1(int x){
        ll ret = 0;
        while (x) {
            ret += bit1[x];
            x &= (x - 1);
        }
        return (ret);
    }
    
    ll sum2(int x){
        ll ret = 0;
        while (x) {
            ret += bit2[x];
            x &= (x - 1);
        }
        return (ret);
    }
    
    ll sum(int x){
        return sum1(x)*x - sum2(x);
    }
    // [l,r]
    ll RangeSum(int l,int r){
        return sum(r) - sum(l-1);
    }
};

template<class Type>
Type solve(Type res = Type()){
    ll N,D,A; cin >> N >> D >> A;
    vector<pll> XH(N);
    vector<ll> CX(N);
    for(int i = 0; i < N;i++){
        cin >> XH[i].first >> XH[i].second;
        CX[i] = XH[i].first;
    }
    sort(XH.begin(),XH.end());
    sort(CX.begin(),CX.end());
    CX.erase(unique(CX.begin(),CX.end()),CX.end());
    
    for(int i = 0; i < N;i++){
        XH[i].first = lower_bound(CX.begin(),CX.end(),XH[i].first) - CX.begin() + 1;
    }
    BIT bit(CX.size());
    for(int i = 0; i < N;i++){
        bit.RangeAdd(XH[i].first,XH[i].first,XH[i].second);
    }
    
    for(int i = 0; i < N;i++){
        ll X,H; tie(X,H) = XH[i];
        ll refH = bit.RangeSum(X,X);
        if(refH <= 0) continue;
        
        res += (refH+A-1)/A;
        ll r = upper_bound(CX.begin(),CX.end(),CX[X-1]+2*D) - CX.begin() + 1;
        
        bit.RangeAdd(X,r-1,-(refH+A-1)/A*A);
    }
    return res;
}
int main(void) {
    cin.tie(0); ios_base::sync_with_stdio(false);
    // solve(0);
    cout << fixed << setprecision(15) << solve<ll>() << endl;
    return 0;
}


Measured memory_bytes: 8064