#include <bits/stdc++.h>
using namespace std;
/*
#if __has_include(<boost/multiprecision/cpp_int.hpp>)
	#include <boost/multiprecision/cpp_int.hpp>
	#include <boost/multiprecision/cpp_dec_float.hpp>
	using bll = boost::multiprecision::cpp_int;
	using bdouble = boost::multiprecision::number<boost::multiprecision::cpp_dec_float<100>>;
	using namespace boost::multiprecision;
#endif
*/
#ifdef LOCAL_TEST
	#define BOOST_STACKTRACE_USE_ADDR2LINE
	#define BOOST_STACKTRACE_ADDR2LINE_LOCATION /usr/local/opt/binutils/bin/addr2line
	#define _GNU_SOURCE 1
	#include <boost/stacktrace.hpp>
	namespace std {
		template<typename T> class dvector : public std::vector<T> {
		public:
			dvector() : std::vector<T>() {}
			explicit dvector(size_t n, const T& value = T()) : std::vector<T>(n, value) {}
			dvector(const std::vector<T>& v) : std::vector<T>(v) {}
			dvector(const std::initializer_list<T> il) : std::vector<T>(il) {}
			dvector(const std::string::iterator first, const std::string::iterator last) : std::vector<T>(first, last) {}
			dvector(const typename std::vector<T>::iterator first, const typename std::vector<T>::iterator last) : std::vector<T>(first, last) {}
			dvector(const typename std::vector<T>::reverse_iterator first, const typename std::vector<T>::reverse_iterator last) : std::vector<T>(first, last) {}
			dvector(const typename std::vector<T>::const_iterator first, const typename std::vector<T>::const_iterator last) : std::vector<T>(first, last) {}
			dvector(const typename std::vector<T>::const_reverse_iterator first, const typename std::vector<T>::const_reverse_iterator last) : std::vector<T>(first, last) {}
			T& operator[](size_t n) {
				try { return this->at(n); } catch (const std::exception& e) { std::cerr << boost::stacktrace::stacktrace() << '\n'; return this->at(n); }
			}
			const T& operator[](size_t n) const {
				try { return this->at(n); } catch (const std::exception& e) { std::cerr << boost::stacktrace::stacktrace() << '\n'; return this->at(n); }
			}
		};
	}
	class dbool {
	private:
		bool boolvalue;
	public:
		dbool() : boolvalue(false) {}
		dbool(bool b) : boolvalue(b) {}
		operator bool&() { return boolvalue; }
		operator const bool&() const { return boolvalue; }
	};
	#define vector dvector
	#define bool dbool
	class SIGFPE_exception : std::exception {};
	class SIGSEGV_exception : std::exception {};
	void catch_SIGFPE([[maybe_unused]] int e) { std::cerr << boost::stacktrace::stacktrace() << '\n'; throw SIGFPE_exception(); }
	void catch_SIGSEGV([[maybe_unused]] int e) { std::cerr << boost::stacktrace::stacktrace() << '\n'; throw SIGSEGV_exception(); }
	signed convertedmain();
	signed main() { signal(SIGFPE, catch_SIGFPE); signal(SIGSEGV, catch_SIGSEGV); return convertedmain(); }
	#define main() convertedmain()
#endif
#ifdef LOCAL_DEV
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::pair<T1, T2>& p) {
		return s << "(" << p.first << ", " << p.second << ")"; }
	template <typename T, size_t N> std::ostream& operator<<(std::ostream& s, const std::array<T, N>& a) {
		s << "{ "; for (size_t i = 0; i < N; ++i){ s << a[i] << "\t"; } s << "}"; return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::set<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}"; return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::multiset<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}"; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::map<T1, T2>& m) {
		s << "{\n"; for (auto itr = m.begin(); itr != m.end(); ++itr){ s << "\t" << (*itr).first << " : " << (*itr).second << "\n"; } s << "}"; return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::deque<T>& v) {
		for (size_t i = 0; i < v.size(); ++i){ s << v[i]; if (i < v.size() - 1) s << "\t"; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::vector<T>& v) {
		for (size_t i = 0; i < v.size(); ++i){ s << v[i]; if (i < v.size() - 1) s << "\t"; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::vector<std::vector<T>>& vv) {
		s << "\\\n"; for (size_t i = 0; i < vv.size(); ++i){ s << vv[i] << "\n"; } return s; }
	void debug_impl() { std::cerr << '\n'; }
	template<typename Head, typename... Tail> void debug_impl(Head head, Tail... tail) { std::cerr << " " << head << (sizeof...(tail) ? "," : ""); debug_impl(tail...); }
	#define debug(...) do { std::cerr << ":" << __LINE__ << " (" << #__VA_ARGS__ << ") ="; debug_impl(__VA_ARGS__); } while (false)
#else
	#define debug(...) do {} while (false)
#endif
//#define int long long
using ll = long long;
//constexpr int INF = (ll)1e9 + 7;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18;//(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr ll dx[4] = {1, 0, -1, 0};
constexpr ll dy[4] = {0, 1, 0, -1};
constexpr ll dx8[8] = {1, 0, -1, 0, 1, 1, -1, -1};
constexpr ll dy8[8] = {0, 1, 0, -1, 1, -1, 1, -1};
#define rep(i, n)   for(ll i=0, i##_length=(n); i< i##_length; ++i)
#define repeq(i, n) for(ll i=1, i##_length=(n); i<=i##_length; ++i)
#define rrep(i, n)   for(ll i=(n)-1; i>=0; --i)
#define rrepeq(i, n) for(ll i=(n)  ; i>=1; --i)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
void p() { std::cout << '\n'; }
template<typename Head, typename... Tail> void p(Head head, Tail... tail) { std::cout << head << (sizeof...(tail) ? " " : ""); p(tail...); }
template<typename T> inline void pv(std::vector<T>& v) { for(ll i=0, N=v.size(); i<N; i++) std::cout << v[i] << " \n"[i==N-1]; }
template<typename T> inline bool chmax(T& a, T b) { return a < b && (a = b, true); }
template<typename T> inline bool chmin(T& a, T b) { return a > b && (a = b, true); }
template<typename T> inline void uniq(std::vector<T>& v) { v.erase(std::unique(v.begin(), v.end()), v.end()); }

/*-----8<-----template-----8<-----*/

//動的セグ木
//https://www.geeksforgeeks.org/dynamic-segment-trees-online-queries-for-range-sum-with-point-updates/
template< typename Monoid, typename OperatorMonoid, typename F, typename G, typename H >
class SegmentTreeDynamicLazy {
public:
	struct Node {
		Monoid value, lazy;
		Node *L, *R, *P;
		Node(): value(0), lazy(0), L(nullptr), R(nullptr), P(nullptr) {}
	};
	ll sz;
	const F f;
	const G g;
	const H h;
	const Monoid M1;
	const OperatorMonoid OM0;
	Node* root;

	SegmentTreeDynamicLazy(ll n, const F &f, const G &g, const H &h, const Monoid &M1, const OperatorMonoid &OM0)
	 : f(f), g(g), h(h), M1(M1), OM0(OM0) {
		sz = 1;
		while(sz < n) sz <<= 1;
		root = createNode();
	}

	Node* createNode() {
		Node* node = new Node();
		node->value = M1;
		node->lazy = OM0;
		return node;
	}

	void update(ll L, ll R, OperatorMonoid value) {
		updateHelper(root, L, R, 0, sz, value);
	}

	Monoid query(ll L, ll R) {
		return queryHelper(root, L, R, 0, sz);
	}

private:
	void eval(Node* curr, ll l, ll r) {
		if (curr->lazy != OM0) {
			curr->value = g(curr->value, curr->lazy);
			if (r - l > 1) {
				if (!curr->L) {
					curr->L = createNode();
					curr->L->P = curr;
				}
				if (!curr->R) {
					curr->R = createNode();
					curr->R->P = curr;
				}
				curr->L->lazy = h(curr->L->lazy, curr->lazy / 2);
				curr->R->lazy = h(curr->R->lazy, curr->lazy / 2);
			}
			curr->lazy = OM0;
		}
	}

	void updateHelper(Node* curr, ll a, ll b, ll L, ll R, OperatorMonoid val) {
		if (b <= L || R <= a) return;
		eval(curr, L, R);
		if (a <= L && R <= b) {
			curr->lazy = h(curr->lazy, val * (R - L));
			eval(curr, L, R);
			return;
		}
		ll mid = L + (R - L) / 2;
		if (!curr->L) curr->L = createNode();
		if (!curr->R) curr->R = createNode();
		updateHelper(curr->L, a, b, L, mid, val);
		updateHelper(curr->R, a, b, mid, R, val);
		Monoid sum1 = M1, sum2 = M1;
		if (curr->L) sum1 = g(curr->L->value, curr->L->lazy);
		if (curr->R) sum2 = g(curr->R->value, curr->R->lazy);
		curr->value = f(sum1, sum2);
	}
	
	Monoid queryHelper(Node* curr, ll a, ll b, ll L, ll R) {
		if (!curr) return M1;
		if (R <= a || b <= L) return M1;
		eval(curr, L, R);
		if (a <= L && R <= b) return curr->value;
		ll mid = L + (R - L) / 2;
		Monoid sum1 = queryHelper(curr->L, a, b, L, mid);
		Monoid sum2 = queryHelper(curr->R, a, b, mid, R);
		return f(sum1, sum2);
	}
};
template< typename Monoid, typename OperatorMonoid, typename F, typename G, typename H >
std::ostream& operator<<(std::ostream& s, SegmentTreeDynamicLazy<Monoid,OperatorMonoid,F,G,H>& seg) { 
	auto dfs = [&](auto&& dfs, ll l, ll r, auto&& curr) -> void {
		s << "\t[" << l << ", " << r << ") : " << curr->value << ", " << curr->lazy << "\n";
		if (l+1==r) s << "\t" << l << " : " << curr->value << ", " << curr->lazy << "\n";
		ll mid = l + (r - l) / 2;
		if (curr->L) dfs(dfs, l, mid, curr->L);
		if (curr->R) dfs(dfs, mid, r, curr->R);
	};
	s << "{\n";
	dfs(dfs, 0, seg.sz, seg.root);
	return s << "}";
}

/*-----8<-----library-----8<-----*/

void solve() {
	ll N,D,A;
	cin>>N>>D>>A;
	vector<pair<ll,ll>> X(N);
	rep(i,N)cin>>X[i].first>>X[i].second;
	sort(all(X));

	auto F = [](ll x,ll y){return x+y;}; 
	SegmentTreeDynamicLazy<ll,ll,decltype(F),decltype(F),decltype(F)> seg((ll)1e9+1, F, F, F, 0LL, 0LL);

	rep(i,N){
		seg.update(X[i].first, X[i].first+1, X[i].second);
	}

	ll ans=0;
	rep(i,N){
		ll nokori=seg.query(X[i].first, X[i].first+1);
		if(nokori<=0)continue;
		ll kaisu=(nokori+A-1)/A;
		ans+=kaisu;
		seg.update(X[i].first, X[i].first+D*2+1, -A*kaisu);
	}
	p(ans);
}

signed main() {
	std::cin.tie(nullptr);
	std::ios::sync_with_stdio(false);
	//ll Q; cin >> Q; while(Q--)solve();
	solve();
	return 0;
}


Measured memory_bytes: 425604