#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <stdlib.h>     /* srand, rand */
#include <time.h>       /* time */
#define mt make_tuple
#define ll long long
#define ld long double
#define eb emplace_back
#define fi first
#define pb push_back
#define endl '\n'
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define forn(i, n) for (int i = 0; i < (int)(n); ++i)
#define fore(i, a, b) for (int i = (int)(a); i <= (int)(b); ++i)
#define scanVec(vec , n) for(int i = 0; i < n ; i++){ scanf("%d",&vec[i]);}
#define printVec(vec , n) for(int i = 0; i < n ; i++){ cout<<vec[i]<<" ";}
#define mod(a,b) ((a%b +b)%b)
#define bit(x,i) (x&(1<<i))  //select the bit of position i of x
#define lowbit(x) ((x)&((x)^((x)-1))) //get the lowest bit of x
#define hBit(msb,n) asm("bsrl %1,%0" : "=r"(msb) : "r"(n)) //get the highest bit of x, maybe the fastest
#define max(a,b) (a<b?b:a)
#define min(a,b) (a>b?b:a) 
//#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }
#define IN(i,l,r) (l<i&&i<r)
#define LINR(i,l,r) (l<=i&&i<=r)
#define LIN(i,l,r) (l<=i&&i<r)
#define INR(i,l,r) (l<i&&i<=r)
#define lastEle(vec) vec[vec.size()-1] 
#define SZ(x) ((int)((x).size()))
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++) 
#define ll long long 
#define ull unsigned long long
#define ui unsigned int
#define us unsigned short
#define INF 1001001001
#define PI 3.1415926535897932384626
 
using namespace std;
 using namespace __gnu_pbds;
 template <typename T>
 using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
 
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpi;
typedef vector<vi> vvi;

/*
void err(istream_iterator<string> it) {}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
    cerr << *it << " = " << a << endl;
    err(++it, args...);
}
 */
//----------------------------------------------------------------------------------------------------------------------
  
void swap(int & a, int & b){
    auto temp = a;
    a = b;
    b = temp;
}
 
const ll MOD = 1e9 + 7;
 
ll inf = 1LL*1e18;
 
void no(){
    cout <<"NO" << endl;
    exit(0);
}
 
void yes(){
    cout <<"YES" << endl; exit(0);
}
 
long long binpow(long long a, long long b, long long m) {
    a %= m;
    long long res = 1;
    while (b > 0) {
        if (b & 1)
            res = res * a % m;
        a = a * a % m;
        b >>= 1;
    }
    return res;
}

// const int MAXN = (1 << 20);
// const int MAXLOG = 20;

// ll dp[MAXN][MAXLOG];
// ll prec_lg2[MAXN], n;
// struct sparse_table
// {
                                                                                      
// 	//sparse_table() { memset(dp, 0, sizeof(dp)); memset(prec_lg2, 0, sizeof(prec_lg2)); n = 0; }

// 	void init(vector<ll> &a)
// 	{
// 		n = a.size();
// 		for(int i = 2; i < 2 * n; i++) prec_lg2[i] = prec_lg2[i >> 1] + 1;
// 		for(int i = 0; i < n; i++) dp[i][0] = a[i];
// 		for(int j = 1; (1 << j) <= n; j++)    
// 			for(int i = 0; i < n; i++)
// 				dp[i][j] = min(dp[i][j - 1], dp[i + (1 << (j - 1))][j - 1]);
// 	}

// 	ll query(ll l, ll r) {
//         if(l > r) return inf;
// 		ll k = prec_lg2[r - l + 1];
// 		return min(dp[l][k], dp[r - (1 << k) + 1][k]);
// 	}
// };


void s(){
	ll n,d,a;
	cin >> n >> d >> a;
	vector< pair< ll , ll > > arr (n);
	for(int i = 0;i < n;i++) cin >> arr[i].first >> arr[i].second;
	sort(all(arr));
	vector< pair< int , ll > > dec;
	ll del = 0;
	ll ans = 0;
	int ind = 0;
	for(int i = 0;i < n;i++){
		while(ind < (int)dec.size() && dec[ind].first < arr[i].first){
			del -= dec[ind].second;
			ind++;
			if(ind == (int)dec.size()) break;
		}
		arr[i].second -= del;
		if(arr[i].second <= 0) continue;
		ll cnt = arr[i].second/a;
		if(arr[i].second%a != 0) cnt++;
		del += cnt*a;
		ans += cnt;
		dec.pb({arr[i].first + 2*d,cnt*a});
	}
	cout << ans << endl;
}

int main(){
	//freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
	ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int t = 0;
    if(t == 1) cin >> t;
    else t = 1;
    while(t--) s();
    return 0;
} 


Measured memory_bytes: 9456