/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author tatsumack
 */

#include <iostream>
#include <fstream>

#include <iostream>
#include <limits.h>
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>

#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <queue>
#include <unordered_map>
#include <unordered_set>

#define int long long
#define REP(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define REPS(i, n) for (int i = 1, i##_len = (n); i <= i##_len; ++i)
#define FOR(i, a, b) for (int i = (a), i##_len = (b); i <= i##_len; ++i)
#define REV(i, a, b) for (int i = (a); i >= (b); --i)
#define CLR(a, b) memset((a), (b), sizeof(a))
#define DUMP(x) cout << #x << " = " << (x) << endl;
#define INF 1001001001001001001ll
#define fcout cout << fixed << setprecision(12)

using namespace std;

typedef pair<int, int> P;

// 区間最大、区間加算
struct LazySegmentTree {
private:
    int n;
    vector<int> node, lazy;

public:
    LazySegmentTree(vector<int> 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] = max(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];
                lazy[2 * k + 2] += lazy[k];
            }
            lazy[k] = 0;
        }
    }

    void add(int a, int b, int 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] += 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] = max(node[2 * k + 1], node[2 * k + 2]);
        }
    }

    int find(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 -INF;
        if (a <= l && r <= b) return node[k];
        int vl = find(a, b, 2 * k + 1, l, (l + r) / 2);
        int vr = find(a, b, 2 * k + 2, (l + r) / 2, r);
        return max(vl, vr);
    }
};

class FSilverFoxVsMonster {
public:
    void solve(std::istream& cin, std::ostream& cout) {
        int N, D, A;
        cin >> N >> D >> A;
        vector<P> v(N);

        REP(i, N) {
            int x, h;
            cin >> x >> h;
            v[i] = {x, h};
        }
        sort(v.begin(), v.end());

        vector<int> X(N), H(N);
        REP(i, N) {
            X[i] = v[i].first;
            H[i] = v[i].second;
        }

        LazySegmentTree seg(H);
        int res = 0;
        REP(i, N) {
            int hp = seg.find(i, i + 1);
            if (hp <= 0) continue;
            int x = X[i];
            int to = upper_bound(X.begin(), X.end(), x + 2 * D) - X.begin();

            int num = (hp + A - 1) / A;
            seg.add(i, to, -A * num);
            res += num;
        }
        cout << res << endl;
    }
};


signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    std::istream& in(std::cin);
    std::ostream& out(std::cout);

    FSilverFoxVsMonster solver;
    solver.solve(in, out);
    return 0;
}


Measured memory_bytes: 16740