#include<iostream>
#include<iomanip>
#include<map>
#include<unordered_map>
#include<set>
#include<vector>
#include<algorithm>
#include<cmath>
#include<string>
#include<queue>
#include<stack>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> pii;
typedef pair<ll, bool> pib;

typedef vector<bool> vb;

typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;

typedef vector<pii> vpii;
typedef vector<vpii> vvpii;

typedef vector<double> vf;

typedef queue<ll> qi;

typedef long double ld;

#define mp make_pair
#define pb push_back

#define rep(i, N) for(ll i = 0; i < N; i++)
#define repa(i, a, N) for(ll i = a; i < N; i++)
#define repr(i, N) for(ll i = N-1; i >= 0; i--)

#define drep(i, N, j, M) rep(i, N) rep(j, M)
#define trep(i, N, j, M, k, L) rep(i, N) rep(j, M) rep(k, L)

#define all(A) A.begin(), A.end()
template<class t, class u>
ostream& operator<<(ostream& os, const pair<t, u>& p) {
	return os << "{" << p.first << "," << p.second << "}";
}

template<class t>
ostream& operator<<(ostream& os, const vector<t>& v) {
	os << "{";
	for (auto e : v)os << e << ",";
	return os << "}";
}

template<class t, class u>
ostream& operator<<(ostream& os, const unordered_map<t, u>& m) {
	os << "{";
	for (auto itr = m.begin(); itr != m.end(); ++itr) {
		os << "(" << itr->first << ", " << itr->second << "), ";
	}
	return os << "}";
}

template<class t>
ostream& operator<<(ostream& os, const set<t>& m) {
	os << "{";
	for (auto itr = m.begin(); itr != m.end(); ++itr) {
		os << *itr << ", ";
	}
	return os << "}";
}

template<class t>
ostream& operator<<(ostream& os, const multiset<t>& m) {
	os << "{";
	for (auto itr = m.begin(); itr != m.end(); ++itr) {
		os << *itr << ", ";
	}
	return os << "}";
}


const ll LLMAX = numeric_limits<long long>::max() / 3;
const double DMAX = numeric_limits<double>::max() / 3;

const double PI = 3.141592653589793;
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;

template <std::int_fast64_t Modulus> class modint {
	using i64 = std::int_fast64_t;

public:
	i64 a;

	constexpr modint(const i64 x = 0) noexcept : a(x % Modulus) {}
	constexpr i64 &value() noexcept { return a; }
	constexpr const i64 &value() const noexcept { return a; }
	constexpr modint operator+(const modint rhs) const noexcept {
		return modint(*this) += rhs;
	}
	constexpr modint operator-(const modint rhs) const noexcept {
		return modint(*this) -= rhs;
	}
	constexpr modint operator*(const modint rhs) const noexcept {
		return modint(*this) *= rhs;
	}
	constexpr modint operator/(const modint rhs) const noexcept {
		return modint(*this) /= rhs;
	}
	constexpr modint &operator+=(const modint rhs) noexcept {
		a += rhs.a;
		if (a >= Modulus) {
			a -= Modulus;
		}
		return *this;
	}
	constexpr modint &operator-=(const modint rhs) noexcept {
		if (a < rhs.a) {
			a += Modulus;
		}
		a -= rhs.a;
		return *this;
	}
	constexpr modint &operator*=(const modint rhs) noexcept {
		a = a * rhs.a % Modulus;
		return *this;
	}
	constexpr modint &operator/=(modint rhs) noexcept {
		i64 exp = Modulus - 2;
		while (exp) {
			if (exp % 2) {
				*this *= rhs;
			}
			rhs *= rhs;
			exp /= 2;
		}
		return *this;
	}
};

template<std::int_fast64_t Modulus>
ostream& operator<<(ostream& os, const modint<Modulus>& m) {
	return os << (m.a + Modulus) % Modulus;
}

typedef modint<MOD> mod;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }


void No() { cout << "No" << endl; }
void Yes() { cout << "Yes" << endl; }
void NO() { cout << "NO" << endl; }
void YES() { cout << "YES" << endl; }

int main() {
	ll N, D, A;
	cin >> N >> D >> A;

	vpii XH(N);

	rep(i, N) {
		ll x, h;
		cin >> x >> h;
		XH[i] = mp(x, h);
	}

	sort(all(XH));

	ll count = 0;
	queue<pii> dq;
	ll ds = 0;
	for(auto xh : XH) {
		ll x, h;
		x = xh.first;
		h = xh.second;

		while (!dq.empty() && dq.front().first < x) {
			ds -= dq.front().second;
			dq.pop();
		}

		h -= ds;
		if (h > 0) {
			ll c = ceil((double)h / A);
			ll damage = c * A;
			count += c;

			dq.push(mp(x + 2*D, damage));
			ds += damage;
		}
	}

	cout << count << endl;
	return 0;
}


Measured memory_bytes: 4992