//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <unordered_map>
#include <climits>
#include <set>
#include <unordered_set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
#include <random>
#include <chrono>
#include <complex>
#include <regex>
#include <locale>
#include <random>
#include <cassert>
#include <type_traits>

using namespace std;

// typedef
//------------------------------------------
typedef long long LL;
typedef vector<int> VI;
typedef vector<bool> VB;
typedef vector<char> VC;
typedef vector<double> VD;
typedef vector<string> VS;
typedef vector<LL> VLL;
typedef vector<VI> VVI;
typedef vector<VB> VVB;
typedef vector<VS> VVS;
typedef vector<VLL> VVLL;
typedef vector<VVI> VVVI;
typedef vector<VVLL> VVVLL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef pair<int, string> PIS;
typedef pair<string, int> PSI;
typedef pair<string, string> PSS;
typedef vector<PII> VPII;
typedef vector<PLL> VPLL;
typedef vector<VPII> VVPII;
typedef vector<VPLL> VVPLL;
typedef vector<VS> VVS;
typedef map<int, int> MII;
typedef map<LL, LL> MLL;
typedef map<string, int> MSI;
typedef map<int, string> MIS;

// container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define EACH(i, arr) for(typeof((arr).begin()) i=(arr).begin(); i!=(arr).end(); ++i)
#define EXIST(str, e) ((str).find(e)!=(str).end())
#define COUNT(arr, v) count((arr).begin(), (arr).end(), v)
#define SEARCH(v, w) search((v).begin(), (v).end(), (w).begin(), (w).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define REVERSE(c) reverse((c).begin(), (c).end())
#define ROTATE_LEFT(arr, c) rotate((arr).begin(), (arr).begin()+(c), (arr).end())
#define ROTATE_RIGHT(arr, c) rotate((arr).rbegin(), (arr).rbegin() + (c), (arr).rend())
#define SUMI(arr) accumulate((arr).begin(), (arr).end(), 0)
#define SUMD(arr) accumulate((arr).begin(), (arr).end(), 0.)
#define SUMLL(arr) accumulate((arr).begin(), (arr).end(), 0LL)
#define MULD(arr) accumulate((arr).begin(), (arr).end(), 1., multiplies<double>())
#define UB(arr, n) upper_bound((arr).begin(), (arr).end(), n)
#define LB(arr, n) lower_bound((arr).begin(), (arr).end(), n)
#define PB push_back
#define MP make_pair
#define ft first
#define sd second


// input output
//------------------------------------------
#define GL(s) getline(cin, (s))
#define INIT() std::ios::sync_with_stdio(false);std::cin.tie(0)
#define OUT(d) std::cout<<(d)
#define OUT_L(d) std::cout<<(d)<<endl
#define FOUT(n, data) std::cout<<std::fixed<<std::setprecision(n)<<(data)
#define FOUT_L(n, data) std::cout<<std::fixed<<std::setprecision(n)<<(data)<<"\n"
#define EL() printf("\n")
#define SHOW_VECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOW_MAP(v) {std::cerr << #v << endl; for(const auto& xxx: v){std::cerr << xxx.first << " " << xxx.second << "\n";}}
#define Yes() printf("Yes\n")
#define No() printf("No\n")
#define YES() printf("YES\n")
#define NO() printf("NO\n")
#define Yay() printf("Yay!\n")
#define Nnn() printf(":(\n")
#define CE(x, y) ((x + y - 1) / (y))


template<typename T1, typename T2>
istream &operator>>(istream &in, pair<T1, T2> &p) {
    in >> p.first >> p.second;
    return in;
}

template<typename T>
istream &operator>>(istream &in, vector<T> &v) {
    for (auto &x: v)
        in >> x;
    return in;
}


template<typename T1, typename T2>
ostream &operator<<(ostream &out, const std::pair<T1, T2> &p) {
    out << "[" << p.first << ", " << p.second << "]" << "\n";
    return out;
}


//repetition
//------------------------------------------
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define RFOR(i, a, b) for(int i=(b)-1;i>=(a);--i)
#define REP(i, n)  FOR(i,0,n)
#define RREP(i, n) for(int i = n-1;i >= 0;i--)
#define FORLL(i, a, b) for(LL i=LL(a);i<LL(b);++i)
#define RFORLL(i, a, b) for(LL i=LL(b)-1;i>=LL(a);--i)
#define REPLL(i, n) for(LL i=0;i<LL(n);++i)
#define RREPLL(i, n) for(LL i=LL(n)-1;i>=0;--i)
#define FOREACH(x, arr) for(auto &(x) : (arr))

//------------------------------------------
//------------------------------------------

template<typename T>
struct LazySegmentTree {

private:
    int n;
    T init_v;
    vector<T> node;
    vector<T> lazy;

public:
    LazySegmentTree(vector<T> a, T _init_v) {

        n = 1;
        init_v = _init_v;

        int sz = a.size();
        while (n < sz) n *= 2;

        node.resize(2 * n, init_v);
        lazy.resize(2 * n, init_v);

        for (int i = 0; i < sz; i++) node[i + n - 1] = a[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[k * 2 + 1] += lazy[k] / 2;
                lazy[k * 2 + 2] += lazy[k] / 2;
            }
            lazy[k] = 0;
        }
    }

    void add(int a, int b, T x, int k = 0, int l = 0, int r = -1) {
        if (r < 0) r = n;
        eval(k, l, r);
        if (r <= a || b <= l) return;
        if (a <= l && r <= b) {
            lazy[k] += (r - l) * x;
            eval(k, l, r);
        } else {
            add(a, b, x, k * 2 + 1, l, (l + r) / 2);
            add(a, b, x, k * 2 + 2, (l + r) / 2, r);
            node[k] = node[k * 2 + 1] + node[k * 2 + 2];
        }
    }

    T getsum(int a, int b, int k = 0, int l = 0, int r = -1) {
        if (r < 0) r = n;
        eval(k, l, r);
        if (r <= a || b <= l) return 0;
        if (a <= l && r <= b) return node[k];
        T lv = getsum(a, b, k * 2 + 1, l, (l + r) / 2);
        T rv = getsum(a, b, k * 2 + 2, (l + r) / 2, r);
        return lv + rv;
    }

};

int main() {

    LL N, D, A;
    cin >> N >> D >> A;
    D *= 2;

    vector<pair<LL, LL>> XH(N);
    REP(i, N) {
        LL x, h;
        cin >> x >> h;
        h = CE(h, A);
        XH[i] = make_pair(x, h);
    }
    sort(XH.begin(), XH.end());

    vector<LL> X(N), H(N);
    REP(i, N) tie(X[i], H[i]) = XH[i];

    LazySegmentTree<LL> tree(vector<LL>(N), 0);
    for (int i = 0; i < N; i++) tree.add(i, i + 1, H[i]);

    LL ans = 0;
    for (int i = 0; i < N; i++) {
        LL val = tree.getsum(i, i + 1);
        if (val <= 0) continue;
        ans += val;
        LL to = upper_bound(X.begin(), X.end(), X[i] + D) - X.begin();
        tree.add(i, to, -val);
    }
    cout << ans << endl;

}
















































Measured memory_bytes: 16256