#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Edge = int;
using Graph = vector<vector<Edge>>;
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define RSORT(v) sort((v).rbegin(), (v).rend())
const ll MOD = 1000000007;
const ll nmax = 8;
const ll INF = 1e9;
bool graph[nmax][nmax];
vector<vector<ll>> dist = vector<vector<ll>>(nmax, vector<ll>(nmax, INF));
struct LazySegmentTree
{
private:
    ll n;
    vector<ll> node, lazy;
    vector<bool> lazyFlag;

public:
    LazySegmentTree(vector<ll> v)
    {
        ll sz = (ll)v.size();
        n = 1;
        while (n < sz)
            n *= 2;
        node.resize(2 * n - 1);
        lazy.resize(2 * n - 1, INF);
        lazyFlag.resize(2 * n - 1, false);

        for (ll i = 0; i < sz; i++)
            node[i + n - 1] = v[i];
        for (ll i = n - 2; i >= 0; i--)
            node[i] = min(node[i * 2 + 1], node[i * 2 + 2]);
    }

    void lazyEvaluate(ll k, ll l, ll r)
    {
        if (lazyFlag[k])
        {
            node[k] = lazy[k];
            if (r - l > 1)
            {
                lazy[k * 2 + 1] = lazy[k * 2 + 2] = lazy[k];
                lazyFlag[k * 2 + 1] = lazyFlag[k * 2 + 2] = true;
            }
            lazyFlag[k] = false;
        }
    }
    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 find(ll a, ll b, ll k = 0, ll l = 0, ll r = -1)
    {
        if (r < 0)
            r = n;
        lazyEvaluate(k, l, r);
        if (b <= l || r <= a)
            return INF;
        if (a <= l && r <= b)
            return node[k];
        ll vl = find(a, b, 2 * k + 1, l, (l + r) / 2);
        ll vr = find(a, b, 2 * k + 2, (l + r) / 2, r);
        return min(vl, vr);
    }
};
void warshall_floyd(ll n)
{
    for (size_t i = 0; i < n; i++)
    {
        for (size_t j = 0; j < n; j++)
        {
            for (size_t k = 0; k < n; k++)
            {
                dist[j][k] = min(dist[j][k], dist[j][i] + dist[i][k]);
            }
        }
    }
}

class UnionFind
{
public:
    vector<ll> Parent;

    UnionFind(ll N)
    {
        Parent = vector<ll>(N, -1);
    }
    ll find(ll A)
    {
        if (Parent[A] < 0)
            return A;
        return Parent[A] = find(Parent[A]);
    }

    ll size(ll A)
    {
        return -Parent[find(A)];
    }

    bool Union(ll A, ll B)
    {
        A = find(A);
        B = find(B);
        if (A == B)
        {
            return false;
        }
        if (size(A) < size(B))
            swap(A, B);

        Parent[A] += Parent[B];
        Parent[B] = A;

        return true;
    }
};

ll gcd(ll a, ll b)
{
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

ll lcm(ll a, ll b)
{
    ll g = gcd(a, b);
    return a / g * b;
}

ll mulMod(ll a, ll b)
{
    return (((a % MOD) * (b % MOD)) % MOD);
}

ll powMod(ll a, ll p)
{
    if (p == 0)
    {
        return 1;
    }
    else if (p % 2 == 0)
    {
        ll half = powMod(a, p / 2);
        return mulMod(half, half);
    }
    else
    {
        return mulMod(powMod(a, p - 1), a);
    }
}

ll ceil(ll a, ll b)
{
    return (a + b - 1) / b;
}

vector<ll> tsort(Graph G)
{
    ll N = G.size();
    vector<ll> in(N);
    for (auto &&edges : G)
    {
        for (auto &&edge : edges)
        {
            in[edge]++;
        }
    }

    queue<int> que;

    for (int i = 0; i < N; i++)
    {
        if (in[i] == 0)
        {
            que.push(i);
        }
    }
    int cnt = 0;
    vector<ll> ans;
    while (!que.empty())
    {
        int v = que.front();
        que.pop();
        ans.push_back(v);
        for (auto &&next : G[v])
        {

            in[next]--;
            if (in[next] == 0)
            {
                que.push(next);
            }
        }
    }
    return ans;
}
Graph G(100);
void treeDFS(int from, int current, int dist, int &maxDist, int &maxVertex)
{
    if (dist > maxDist)
    {
        maxDist = dist;
        maxVertex = current;
    }

    for (auto to : G[current])
    {
        if (to == from)
            continue;
        treeDFS(current, to, dist + 1, maxDist, maxVertex);
    }
}

pair<int, int> getTreeDiameter()
{
    int start = 0, end = 0, maxDist = 0;
    treeDFS(-1, start, 0, maxDist, end);
    start = end, end = 0, maxDist = 0;
    treeDFS(-1, start, 0, maxDist, end);
    return make_pair(start, end);
}

int main()
{
    ll N, D, A;
    scanf("%lld", &N);
    scanf("%lld", &D);
    scanf("%lld", &A);

    vector<ll> X(N);
    vector<ll> H(N);

    for (int i = 0; i < N; i++)
    {
        cin >> X[i] >> H[i];
    }
    vector<int> ids(N);
    for (int i = 0; i < N; ++i)
        ids[i] = i;
    sort(ids.begin(), ids.end(), [&](int i, int j) { return X[i] < X[j]; });
    vector<long long> nX(N), nH(N);
    for (int i = 0; i < N; ++i)
        nX[i] = X[ids[i]], nH[i] = H[ids[i]];
    X = nX, H = nH;
    SORT(X);
    ll ans = 0;
    vector<ll> S(N + 1, 0);
    for (int i = 0; i < N; i++)
    {
        if (S[i] < H[i])
        {
            ll remain = ceil(H[i] - S[i], A);

            ll right = X[i] + D * 2;
            int id = upper_bound(X.begin(), X.end(), right) - X.begin();

            S[i] += remain * A;
            S[id] -= remain * A;
            ans += remain;
        }
        S[i+1] += S[i];
        
    }

    cout << ans << endl;

    return 0;
}


Measured memory_bytes: 8832