// Goods things are coming, just keep believing 
 
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace __gnu_pbds;
using namespace std;
 
 
#define FOR(i, x, n) for(ll i = x; i < n; i++) 
#define pb push_back
#define pf push_front
#define ll long long
#define hii cout << "hii" << endl
#define okay cout << "okay" << endl
// #define hey cout << "hey" << endl
#define pii pair<int, int>
#define pll pair<ll, ll>
#define mp make_pair
#define endl '\n'
#define ff first 
#define int long long
#define ss second
#define vi vector<int>
#define all(s) s.begin(), s.end()
#define si size()
 #define ld long double
#define INF 1000000000;
 
template <class T> ostream& operator << (ostream &os, const vector<T> &v) { for (T i : v) os << i << ' '; return os; }
template <class T> ostream& operator << (ostream &os, const set<T> &v) { for (T i : v) os << i << ' '; return os; }
template <class T, class S> ostream& operator << (ostream &os, const pair<T, S> &v) { os << v.first << ' ' << v.second; return os; }
template <class T, class S> ostream& operator << (ostream &os, const unordered_map<T, S> &v) { for (auto i : v) os << '(' << i.first << "=>" << i.second << ')' << ' '; return os; } 
 
 
 
#ifndef ONLINE_JUDGE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
    template <class Arg1> void __f(const char* name, Arg1&& arg1) { cerr << name << " : " << arg1 << endl; }
    template <class Arg1, class... Args>
    void __f(const char* names, Arg1&& arg1, Args&&... args) {
        const char* sep = strchr(names + 1, ',');
        cerr.write(names, sep - names) << " : " << arg1 << "  ";
        __f(sep + 1, args...);
    }
#else
#define trace(...) 0
#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx2,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define _CRT_SECURE_NO_WARNINGS
#endif // ifndef ONLINE_JUDGE
 
typedef tree<
int,
null_type,
less<int>,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
 
 
 
const int N = 2e5 + 5;
const int LG = 20;
const int mod = 1e9 + 7;

int arr[N];
vector<pair<int, int>> v;

struct BIT
{
	int N;
	vector<int> bit;

	void init(int n)
	{
		N = n;
		bit.assign(n + 1, 0);
	}

	void update(int idx, int val)
	{
		while(idx <= N)
		{
			bit[idx] += val;
			idx += idx & -idx;
		}
	}

	void updateMax(int idx, int val)
	{
		while(idx <= N)
		{
			bit[idx] = max(bit[idx], val);
			idx += idx & -idx;
		}
	}

	int pref(int idx)
	{
		int ans = 0;
		while(idx > 0)
		{
			ans += bit[idx];
			idx -= idx & -idx;
		}
		return ans;
	}

	int rsum(int l, int r)
	{
		return pref(r) - pref(l - 1);
	}

	int prefMax(int idx)
	{
		int ans = -2e9;
		while(idx > 0)
		{
			ans = max(ans, bit[idx]);
			idx -= idx & -idx;
		}
		return ans;
	}
};


void solve()
{
	BIT btree;
	int n, d, a;
	cin >> n >> d >> a;
	btree.init(n + 5);
	v.push_back({-1, -1});
	for(int i = 0; i < n; i++)
	{
		int x, h;
		cin >> x >> h;
		v.push_back({x, h});
	}
	sort(all(v));
	int cnt = 0;
	for(int i = 1; i <= n; i++)
	{
		int health = v[i].second + btree.pref(i);
		if(health <= 0)
		{
			continue;
		}
		int rounds = (health + a - 1) / a;
		cnt += rounds;
		int pos1 = v[i].first + d;
		int pos2 = pos1 + d;
		int s = i;
		int e = n;
		while(s <= e)
		{
			int mid = s + e >> 1;
			if(v[mid].first <= pos2)
			{
				s = mid + 1;
			}
			else
			{
				e = mid - 1;
			}
		}
		// trace(i, health, s);
		btree.update(i, -(rounds * a));
		btree.update(s, rounds * a);
	}
	cout << cnt << endl;
}

 
int32_t main()
{
	ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);

	int t = 1;
	// cin >> t;
	while(t--)
	{
		solve();
	}
}

Measured memory_bytes: 7920