#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define FASTIO
#define endl "\n"  // Since endl forces a buffer flush which slows down large I/O operations.
#define ff first
#define ss second
#define pb push_back
#define input(c, n) for (int i = 0; i < n; ++i) cin >> c[i];
#define exit_message(s) return 0 * printf(s)
#define show_all(c) for (auto i: c) cout << i << " "; cout << "\n";
#define display(c, a, n) cout << "Displaying array \"" << #c << "\" : \n"; for (int (i) = (a); (i) < (n); ++(i)) cout << (c)[(i)] << " "; cout << "\n";
#define forl(i, a, n) for (int i = (a); (i) < (n); ++(i))
#define dugbe(k) cerr << "-\t> " << #k << " = " << k << "\n";
#define dugbev(arr, idx) cerr << "-\t " << #arr << "[" << idx << "] : " << arr[idx] << "\n";
#define debug(args...) { string _debug_list = #args; replace(_debug_list.begin(), _debug_list.end(), ',', ' '); stringstream _debug_stream(_debug_list); istream_iterator<string> __it(_debug_stream); debug_func(__it, args); }

/*
// What follows is a magical ordered set data structure.
// Supports the following functions:
// find_by_order(int k) - returns k'th smallest element (0-indexed)
// order_of_key(int k) - returns number of elements strictly smaller than k.
using namespace __gnu_pbds;
#define ordered_set tree <ll, null_type, greater_equal <ll>, rb_tree_tag, tree_order_statistics_node_update>
*/

/* TIPS FOR DEBUGGING
 * Check if values are not overflowing (use long long where required)
 * Check if ranges are inclusive or not.
 * Check properly if greedy will work or not before using it.
 * Check EDGE CASES!! Seriously, even in 2B, saving 8 points by being
 * 2 minutes faster will bite you in the ass if you don't make sure
 * it works on edge cases.
 * Keep adding to this list.
*/

using namespace std;
typedef long long ll;
typedef pair<int, int> pr;
typedef pair<ll, ll> prll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<pr> vpr;
ifstream in("input.txt");
const ll mod = 7340033;
const long double eps = 1e-7;

void debug_func(istream_iterator<string> _it)
{
	cerr << "\n";
}

template <typename T, typename... Args>
void debug_func(istream_iterator<string> _it, T x, Args... args)
{
	cerr << "[ " << *_it << " : " << x << " ]";
	cerr << " , ";
	debug_func(++_it, args...);
}

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

long long true_rand(long long n)
{
	// Returns a random number between 0 and n - 1 inclusive using mt19937.
    uniform_int_distribution<long long> uid(0, n - 1);
    return uid(rng);
}

ll mod_pow(ll a, ll b)
{
	if (b == 0)
		return 1LL;

	ll res = mod_pow(a, b >> 1);
	res = (res * res) % mod;
	if (b & 1LL)
		res = (res * a) % mod;
	
	return res;
}

ll inverse(ll a)
{
	return mod_pow(a, mod - 2);
}

const int N = 1e4 + 5;
const ll INF = 1e9 + 5, LLINF = 1e18 + 5;
const int M = 1e6 + 5;

int32_t main()
{
	#ifdef FASTIO
		ios_base::sync_with_stdio(false);
		cin.tie(NULL);
	#endif
	// freopen("input.txt", "r", stdin);
	// freopen("output.txt", "w", stdout);

	ll n, d, a;
	cin >> n >> d >> a;
	vector<prll> p(n);
	forl(i, 0, n)
	{
		cin >> p[i].ff >> p[i].ss;
	}
	sort(p.begin(), p.end());

	ll roll = 0;
	ll bombs = 0;
	vll change(n + 5, 0);
	forl(i, 0, n)
	{
		roll += change[i];
		assert(roll >= 0);

		ll hits = (p[i].ss + a - 1) / a;
		hits -= roll;

		if (hits <= 0)
			continue;

		bombs += hits;
		// debug(i, roll, hits);
		// dugbev(change, i);

		ll rig = p[i].ff + 2 * d;

		int lo = 0, hi = n - 1;
		while (lo <= hi)
		{
			int mid = (lo + hi) >> 1;
			if (p[mid].ff <= rig)
				lo = mid + 1;
			else
				hi = mid - 1;
		}

		roll += hits;
		change[lo] -= hits;
	}

	cout << bombs << "\n";

	return 0;
}

Measured memory_bytes: 4992