#include <bits/stdc++.h>
#ifdef __LOCAL
    #define DBG(X) cout << #X << " = " << (X) << endl;
    #define SAY(X) cout << (X) << endl;
#else
    #define DBG(X)
    #define SAY(X)
#endif

#ifdef __LOCAL
    #include <filesystem>
    namespace fs = std::filesystem;
#endif

using namespace std;

using ll = long long int;
using pll = pair<ll, ll>;

inline void fast_io() { ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); };
template<typename T, typename S> inline ostream& operator<<(ostream& os, const pair<T, S> p) { cout << "[" << p.first << ";" << p.second << "]"; return os; }
template<typename T, typename S> inline ostream& operator<<(ostream& os, const map<T, S> p) { for (auto el : p) os << "[" << el.first << " " << el.second << "]"; return os; }
template<typename T> inline ostream& operator<<(ostream& os, const vector<T>& v) { for (auto el : v) os << el << " "; return os; }
template<typename T> inline vector<T> fetch_vec(int sz) { vector<T> ret(sz); for (auto& elem : ret) cin >> elem; return ret; }

// Segment Tree
template<class Monoid, class Action> struct SegTree {
    using FuncMonoid = function< Monoid(Monoid, Monoid) >;
    using FuncAction = function< void(Monoid&, Action) >;
    using FuncLazy = function< void(Action&, Action) >;
    FuncMonoid FM;
    FuncAction FA;
    FuncLazy FL;
    Monoid UNITY_MONOID;
    Action UNITY_LAZY;
    int SIZE, HEIGHT;
    vector<Monoid> dat;
    vector<Action> lazy;
    
    SegTree() { }
    SegTree(int n, const FuncMonoid fm, const FuncAction fa, const FuncLazy fl,
            const Monoid &unity_monoid, const Action &unity_lazy)
    : FM(fm), FA(fa), FL(fl), UNITY_MONOID(unity_monoid), UNITY_LAZY(unity_lazy) {
        SIZE = 1; HEIGHT = 0;
        while (SIZE < n) SIZE <<= 1, ++HEIGHT;
        dat.assign(SIZE * 2, UNITY_MONOID);
        lazy.assign(SIZE * 2, UNITY_LAZY);
    }
    void init(int n, const FuncMonoid fm, const FuncAction fa, const FuncLazy fl,
              const Monoid &unity_monoid, const Action &unity_lazy) {
        FM = fm; FA = fa; FL = fl;
        UNITY_MONOID = unity_monoid; UNITY_LAZY = unity_lazy;
        SIZE = 1; HEIGHT = 0;
        while (SIZE < n) SIZE <<= 1, ++HEIGHT;
        dat.assign(SIZE * 2, UNITY_MONOID);
        lazy.assign(SIZE * 2, UNITY_LAZY);
    }
    
    /* set, a is 0-indexed */
    void set(int a, const Monoid &v) { dat[a + SIZE] = v; }
    void build() {
        for (int k = SIZE - 1; k > 0; --k)
            dat[k] = FM(dat[k*2], dat[k*2+1]);
    }
    
    /* update [a, b) */
    inline void evaluate(int k) {
        if (lazy[k] == UNITY_LAZY) return;
        if (k < SIZE) FL(lazy[k*2], lazy[k]), FL(lazy[k*2+1], lazy[k]);
        FA(dat[k], lazy[k]);
        lazy[k] = UNITY_LAZY;
    }
    inline void update(int a, int b, const Action &v, int k, int l, int r) {
        evaluate(k);
        if (a <= l && r <= b)  FL(lazy[k], v), evaluate(k);
        else if (a < r && l < b) {
            update(a, b, v, k*2, l, (l+r)>>1), update(a, b, v, k*2+1, (l+r)>>1, r);
            dat[k] = FM(dat[k*2], dat[k*2+1]);
        }
    }
    inline void update(int a, int b, const Action &v) { update(a, b, v, 1, 0, SIZE); }
    
    /* get [a, b) */
    inline Monoid get(int a, int b, int k, int l, int r) {
        evaluate(k);
        if (a <= l && r <= b)
            return dat[k];
        else if (a < r && l < b)
            return FM(get(a, b, k*2, l, (l+r)>>1), get(a, b, k*2+1, (l+r)>>1, r));
        else
            return UNITY_MONOID;
    }
    inline Monoid get(int a, int b) { return get(a, b, 1, 0, SIZE); }
    inline Monoid operator [] (int a) { return get(a, a+1); }
    
    /* debug */
    void print() {
        for (int i = 0; i < SIZE; ++i) { cout << (*this)[i]; if (i != SIZE) cout << ","; }
        cout << endl;
    }
};

ll N,D,A;
struct Monster{
    ll x,h;
    Monster(ll x, ll h):x(x),h(h){};
};
vector<Monster> M;

void input(){
    fast_io();
    #ifdef __LOCAL
        fs::path p = __FILE__;
        fs::path input,output;
        input = output = p.parent_path();
        input += string("/input/") + string(p.stem()) + string(".txt");
        output += string("/output/") + string(p.stem()) + string(".txt");
        freopen(input.c_str(), "r", stdin);
        freopen(output.c_str(), "w", stdout);
    #endif
    cin >> N >> D >> A;
    for(int i=0;i<N;i++){
        ll x, h; cin >> x >> h;
        // h = (h+A-1)/A;
        M.push_back(Monster(x,h));
    }
    sort(M.begin(),M.end(),[](Monster a, Monster b){return a.x < b.x;});
}

ll TLEsolve(){
    int j=0;
    vector<int> L;
    for(int i=0;i<N;i++){
        while(j<N && abs(M[j].x-M[i].x) <= 2*D){j++;}
        L.push_back(j-1);
    }

    ll ans=0LL;
    for(int i=0;i<N;i++){
        if(M[i].h <= 0LL) continue;
        ll n = (M[i].h+A-1)/A;
        ans += n;
        for(int j=i;j<=L[i];j++) M[j].h = max(0LL,M[j].h-n*A);
    }
    return ans;
}

int solve(){
    auto fm = [](long long a, long long b) { return a+b; };
    auto fa = [](long long &a, long long d) { a += d; };
    auto fl = [](long long &d, long long e) { d += e; };
    SegTree<long long, long long> seg(N+1, fm, fa, fl, 0, 0);
    for (int i = 0; i < N; ++i) seg.set(i, M[i].h);
    seg.build();

    int j=0;
    vector<int> L;
    for(int i=0;i<N;i++){
        while(j<N && abs(M[j].x-M[i].x) <= 2*D){j++;}
        L.push_back(j-1);
    }
    ll ans=0LL;
    for(int i=0;i<N;i++){
        if(seg.get(i,i+1) <= 0LL) continue;
        ll n = (seg.get(i,i+1)+A-1)/A;
        ans += n;
        seg.update(i,L[i]+1,-n*A);
    }
    cout << ans << endl;
    return 0;
}

int main()
{
    input();
    solve();
    return 0;
}


Measured memory_bytes: 14316