#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
const int inf = 1e9 + 7;
const ll INF = 1e18;
#define abs(x) (x >= 0 ? x : -(x))
#define lb(v, x) (int)(lower_bound(all(v), x) - v.begin())
#define ub(v, x) (int)(upper_bound(all(v), x) - v.begin())
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { if (a > b) { a = b; return 1; } return 0; }
template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { if (a < b) { a = b; return 1; } return 0; }
template<typename T> T gcd(T a, T b) { if (b == 0) return a; return gcd(b, a % b); }
template<typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template<typename T> T pow(T a, int b) { return b ? pow(a * a, b / 2) * (b % 2 ? a : 1) : 1; }
const int mod = 1000000007;
ll modpow(ll a, int b) { return b ? modpow(a * a % mod, b / 2) * (b % 2 ? a : 1) % mod : 1; }
template<class T> ostream& operator<<(ostream& os, const vector<T>& vec) { for (auto &vi: vec) os << vi << " "; return os; }

void solve();

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    
    int T;
    // cin >> T;
    T = 1;
    
    while (T--) {
        solve();
    }
}


struct LazySegmentTree {
private:
    int n;
    vector<ll> node, lazy;
    
public:
    LazySegmentTree(vector<ll> v) {
        int sz = (int)v.size();
        n = 1; while(n < sz) n *= 2;
        node.resize(2*n-1);
        lazy.resize(2*n-1, 0);
        
        for(int i=0; i<sz; i++) node[i+n-1] = v[i];
        for(int i=n-2; i>=0; i--) node[i] = node[i*2+1] + node[i*2+2];
    }
    
    void eval(int k, int l, int r) {
        if(lazy[k] != 0) {
            node[k] += lazy[k];
            if(r - l > 1) {
                lazy[2*k+1] += lazy[k] / 2;
                lazy[2*k+2] += lazy[k] / 2;
            }
            lazy[k] = 0;
        }
    }
    
    void add(int a, int b, ll x, int k=0, int l=0, int r=-1) {
        if(r < 0) r = n;
        eval(k, l, r);
        if(b <= l || r <= a) return;
        if(a <= l && r <= b) {
            lazy[k] += (r - l) * x;
            eval(k, l, r);
        }
        else {
            add(a, b, x, 2*k+1, l, (l+r)/2);
            add(a, b, x, 2*k+2, (l+r)/2, r);
            node[k] = node[2*k+1] + node[2*k+2];
        }
    }
    
    ll getsum(int a, int b, int k=0, int l=0, int r=-1) {
        if(r < 0) r = n;
        eval(k, l, r);
        if(b <= l || r <= a) return 0;
        if(a <= l && r <= b) return node[k];
        ll vl = getsum(a, b, 2*k+1, l, (l+r)/2);
        ll vr = getsum(a, b, 2*k+2, (l+r)/2, r);
        return vl + vr;
    }
    
    
};

void solve() {
    ll n, d, a;
    cin >> n >> d >> a;
    LazySegmentTree seg(vector<ll>(n, 0));
    
    vector<pii> tmp(n);
    rep(i, n) cin >> tmp[i].F >> tmp[i].S;
    sort(all(tmp));
    
    vector<ll> x(n);
    rep(i, n) {
        x[i] = tmp[i].F;
        seg.add(i, i + 1, tmp[i].S);
    }
    ll cnt = 0;
    rep(i, n) {
        if (seg.getsum(i, i + 1) <= 0) continue;
        ll kai = (seg.getsum(i, i + 1) + a - 1) / a;
        // cout << i << " " << kai << endl;
        cnt += kai;
        int it = ub(x, x[i] + 2 * d);
        it--;
        // cout << it << endl;
        seg.add(i, it + 1, -kai * a);
    }
    cout << cnt << endl;
}


Measured memory_bytes: 11620