#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

// 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;
    }
};




signed main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);

    ll n,d,a;
    cin>>n>>d>>a;
    auto fm = [](ll a, ll b) { return max(a, b); };
    auto fa = [](ll &a, ll d) { a = a+d; };
    auto fl = [](ll &d, ll e) { d = d+e; };
    SegTree<ll, ll> seg(n+2, fm, fa, fl, 0, 0);
    array<ll,2> x[n];
    map<ll,ll> mp;
    for(int i=0;i<n;i++){
        ll p,h;
        cin>>p>>h;
        x[i] = {p,h};
        mp[p]=1;
    }
    sort(x,x+n);
    ll ans = 0;
    ll cnt = 0;
    vector<ll> v;
    mp[1e15];
    for(auto &i:mp){
        i.second = cnt;
        cnt++;
        v.push_back(i.first);
    }
    v.push_back(1e15);
    for(int i=0;i<n;i++){
        seg.update(i,i+1,x[i][1]);
    }
    for(int i=0;i<n;i++){
        ll ret = seg.get(i,i+1);
        cerr << i << " "<< ret << endl;
        if(ret<=0) continue;
        auto p = upper_bound(v.begin(),v.end(), x[i][0]+2*d);
        p--;
        ll t = mp[*p];
        t++;
        //cerr << *p << " " << t << " " << i << " " << v[i] << " " << x[i][0]<<endl;
        ret = (ret+a-1)/a;
        ans += ret;
        seg.update(i,t,-ret*a);
    }
    cout << ans << endl;


    
}


Measured memory_bytes: 26356