#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<(n); ++i)
#define rep2(i, s, n) for(int i=s; i<(n); ++i)
#define ALL(v) (v).begin(), (v).end()

using namespace std;

typedef long long ll;

static const int INTINF = (2147483647 >> 1); // 10^9 + 5000
static const ll LLINF = (9223372036854775807 >> 1);
static const int MAX = 1e5+1;
static const ll MOD = 1e9+7;

namespace Kunitaka{
    template<
        typename TYPE,
        std::size_t SIZE
    >
    std::size_t array_length(const TYPE (&array)[SIZE])
    {
        return SIZE;
    }
}
using namespace Kunitaka;
namespace Printer{
    void br(){
        cout << endl;
    }

    void loop_cnt(int i){
        cout << "i = " << i << endl;
    }

    void loop_cnt(int i, int j){
        cout << "i = " << i << ", " << "j = " << j << endl;
    }

    template<class T>
    void print(T x){
        cout << x << endl;
    }

    template<class T, class S>
    void print(T x, S y){
        cout << x << "," << y << endl;
    }

    template<class T, class S, class U>
    void print(T x, S y, U z){
        cout << x << "," << y << "," << z << endl;
    }

    template<class T, class S>
    void print(pair<T, S> p){
        cout << p.first << ", " << p.second << endl;
    }

    template<
        typename TYPE,
        std::size_t SIZE
    >
    void print(const TYPE (&array)[SIZE]){
        int lim = array_length(array);
        for(int i=0; i<lim; i++){
            if(i) cout << " ";
            cout << array[i];
        }
        cout << endl;
    }

    template<class T>
    void print(vector<T> v){
        for(int i=0; i<v.size(); i++){
            if(i) cout << " ";
            cout<< v[i];
        }
        cout << endl;
    }

    template<class T>
    void print(vector<vector<T> > vv){
        for(int i=0; i<vv.size(); i++){
            for(int j=0; j<vv[i].size(); j++){
                if(j) cout << " ";
                cout << vv[i][j];
            }
            cout << endl;
        }
    }
};
using namespace Printer;

class LazySegmentTree {
    private:
        int n;
        vector<ll> node, lazy;

    public:
        void init(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 argc, const char * argv[]) {
    //提出時、消す----//
    //--------------//

    // variable
    ll ans = 0;
    LazySegmentTree LST;

    // input
    cout << fixed << setprecision(10);
    ll N, D, A; cin >> N >> D >> A;
    vector<ll> X(N), H(N);
    vector<pair<ll, ll> > XH(N);
    rep(i, N){
        ll x, h; cin >> x >> h;
        XH[i] = make_pair(x, h);
    }
    sort(ALL(XH));
    rep(i, N){
        X[i] = XH[i].first;
        H[i] = XH[i].second;
    }

    // solve
    vector<ll> dummy(N);
    fill(ALL(dummy), 0);
    LST.init(dummy);
    rep(i, N){
        //loop_cnt(i);
        ll rest = H[i] - LST.getsum(i, i+1);
        //print(rest);
        if(rest <= 0) continue;
        ll bomb = X[i] + D;
        auto it = upper_bound(ALL(X), bomb+D);
        int dist = distance(X.begin(), it) - 1;
        ll cnt = rest / A;
        if(rest % A) cnt++;
        LST.add(0, dist+1, A * cnt);
        ans += cnt;
    }
    
    //br();
    print(ans);
    
    return 0;
}


Measured memory_bytes: 17792