#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for(int i=0; i < (n); ++i)
#define ll long long

const int mod = 1000000007;
//const int mod = 998244353;

struct mint {
    ll x; // typedef long long ll;
    mint(ll x=0):x((x%mod+mod)%mod){}
    mint operator-() const { return mint(-x);}
    mint& operator+=(const mint a) {
        if ((x += a.x) >= mod) x -= mod;
        return *this;
    }
    mint& operator-=(const mint a) {
        if ((x += mod-a.x) >= mod) x -= mod;
        return *this;
    }
    mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this;}
    mint operator+(const mint a) const { return mint(*this) += a;}
    mint operator-(const mint a) const { return mint(*this) -= a;}
    mint operator*(const mint a) const { return mint(*this) *= a;}
    mint pow(ll t) const {
        if (!t) return 1;
        mint a = pow(t>>1);
        a *= a;
        if (t&1) a *= *this;
        return a;
    }

    // for prime mod
    mint inv() const { return pow(mod-2);}
    mint& operator/=(const mint a) { return *this *= a.inv();}
    mint operator/(const mint a) const { return mint(*this) /= a;}
};
istream& operator>>(istream& is, const mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}


template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; }}
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; }}

ll gcd(ll a, ll b) { return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b) { return a/gcd(a,b)*b;}

// combination mod prime
// https://www.youtube.com/watch?v=8uowVvQ_-Mo&feature=youtu.be&t=1619
struct combination {
    vector<mint> fact, ifact;
    combination(int n):fact(n+1),ifact(n+1) {
        assert(n < mod);
        fact[0] = 1;
        for (int i = 1; i <= n; ++i) fact[i] = fact[i-1]*i;
        ifact[n] = fact[n].inv();
        for (int i = n; i >= 1; --i) ifact[i-1] = ifact[i]*i;
    }
    mint operator()(int n, int k) {
        if (k < 0 || k > n) return 0;
        return fact[n]*ifact[k]*ifact[n-k];
    }
};
//int main() {
//    ios::sync_with_stdio(false);
//    cin.tie(0);
//
//    ll N, D, A; cin >> N >> D >> A;
//
//    vector< pair<ll, ll> > enemies(N);
//    rep(i, N) cin >> enemies[i].first >> enemies[i].second;
//
//    sort(enemies.begin(), enemies.end());
//    ll ans = 0;
//    int l = 0;
//    while(l < N) {
//        pair<ll, ll> enemy = enemies[l];
//        int atk_cnt = ceil((double) enemy.second / A);
//        ans += atk_cnt;
//        for(int i = l+1; enemies[i].first <= enemy.first + 2 * D; ++i) {
//            enemies[i].second -= A * atk_cnt;
//        }
//        ++l;
//        while(enemies[l].second <= 0 && l < N) ++l;
//    }
//    cout << ans << endl;
//}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int N, D, A; cin >> N >> D >> A;
    vector< pair<int, int> > enemies(N); rep(i, N) cin >> enemies[i].first >> enemies[i].second;
    sort(enemies.begin(), enemies.end());

    ll tot = 0, ans = 0;
    queue< pair<ll, ll> > q;

    rep(i, N) {
        int x = enemies[i].first;
        int h = enemies[i].second;
        while(!q.empty() && q.front().first < x) {
            tot -= q.front().second;
            q.pop();
        }
        h -= tot;
        if (h > 0) {
            int atk_cnt = (h + A - 1) / A;
            ans += atk_cnt;
            ll atk = A * atk_cnt;
            tot += atk;
            q.emplace(x+2*D, atk);
        }
    }
    cout << ans << endl;
}


Measured memory_bytes: 3456