#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define POW2(n) (1LL << (n))
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (q < m) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;


// 1-indexed BIT (i : [1, len])
template<typename T>
struct BIT : std::vector<T>
{
    BIT(int len = 0) : std::vector<T>(len + 1) {}
    void reset() { fill(this->begin(), this->end(), 0); }
    void add(int pos, T v) {
        while (pos > 0 and pos < (int)this->size()) (*this)[pos] += v, pos += pos & -pos;
    }
    T sum(int pos) const { // (0, pos]
        T res = 0;
        while (pos > 0) res += (*this)[pos], pos -= pos & -pos;
        return res;
    }
    friend std::ostream &operator<<(std::ostream &os, const BIT &bit) {
        T prv = 0;
        os << '[';
        for (int i = 1; i < (int)bit.size(); i++) {
            T now = bit.sum(i);
            os << now - prv << ",";
            prv = now;
        }
        os << ']';
        return os;
    }
};

int main()
{
    int N;
    cin >> N;
    lint D, A;
    cin >> D >> A;
    vector<plint> X(N);
    REP(i, N) {
        lint h;
        cin >> X[i].first >> h;
        X[i].second = (h + A - 1) / A;
    }
    sort(ALL(X));
    BIT<lint> bakuha(N + 1);
    lint ret = 0;
    REP(i, N)
    {
        int t = bakuha.sum(i + 1);
        lint req = max(0LL, X[i].second - t);
        ret += req;
        lint r = upper_bound(ALL(X), plint(X[i].first + D * 2, 1e18)) - X.begin();
        bakuha.add(i + 1, req);
        bakuha.add(r + 1, -req);
    }
    cout << ret << endl;
}


Measured memory_bytes: 4992