using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Runtime.CompilerServices;
using System.Text;
using static Template;
using static System.Console;
using static System.Convert;
using static System.Math;
using Pi = Pair<int, int>;

class Solver
{
    public void Solve(Scanner sc)
    {
        int N, D, A;
        sc.Make(out N, out D, out A);
        var xh = sc.ArrInt2D(N);
        Array.Sort(xh,(a,b)=>a[0]-b[0]);
        var res = 0L;
        var idx = 0;
        var seg = new DualSegmentTree<long>(N, 0, (a, b) => a + b);
        for (var i = 0; i < N; i++)
        {
            chmax(ref idx, i); var r = xh[i][1] - seg.Query(i);
            if (r <= 0) continue;
            while (idx != N && xh[i][0] + 2*D >= xh[idx][0])
                idx++;
            seg.Update(i, idx, (r + A - 1) / A * A);
            res += (r + A - 1) / A;
        }
        WriteLine(res);
    }
}


public class DualSegmentTree<T>
{
    protected readonly T[] data;
    protected readonly int size;
    protected readonly Func<T, T, T> merge;
    protected readonly T idT;

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    protected int Parent(int i)
        => (i - 1) >> 1;
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    protected int Left(int i)
        => (i << 1) + 1;
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    protected int Right(int i)
        => (i + 1) << 1;
    public T this[int i]
    {
        get { return data[i + size - 1]; }
        set { data[i + size - 1] = value; }
    }

    public DualSegmentTree(int N, T idT, Func<T, T, T> merge)
    {
        this.merge = merge;
        this.size = 1;
        this.idT = idT;
        while (size < N)
            size <<= 1;
        data = new T[2 * this.size - 1];
        for (var i = 0; i < 2 * size - 1; i++)
            data[i] = idT;
    }
    public void Update(int left, int right, T value, int k = 0, int l = 0, int r = -1)
    {
        if (r == -1) r = size;
        if (r <= left || right <= l) return;
        if (left <= l && r <= right) data[k] = merge(data[k], value);
        else
        {
            Update(left, right, value, Left(k), l, (l + r) >> 1);
            Update(left, right, value, Right(k), (l + r) >> 1, r);
        }
    }
    public T Query(int i)
    {
        i += size - 1;
        var value = merge(idT, data[i]);
        while (i > 0)
        {
            i = Parent(i);
            value = merge(value, data[i]);
        }
        return value;
    }

    public int Find(int st, Func<T, bool> check)
    {
        var x = idT;
        return Find(st, check, ref x, 0, 0, size);
    }
    private int Find(int st, Func<T, bool> check, ref T x, int k, int l, int r)
    {
        if (l + 1 == r)
        { x = merge(x, data[k]); return check(x) ? k - size + 1 : -1; }
        var m = (l + r) >> 1;
        if (m <= st) return Find(st, check, ref x, Right(k), m, r);
        if (st <= l && !check(merge(x, data[k])))
        { x = merge(x, data[k]); return -1; }
        var xl = Find(st, check, ref x, Left(k), l, m);
        if (xl >= 0) return xl;
        return Find(st, check, ref x, Right(k), m, r);
    }
}
#region Template
public static class Template
{
    static void Main(string[] args)
    {
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        new Solver().Solve(new Scanner());
        Console.Out.Flush();
    }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static bool chmin<T>(ref T a, T b) where T : IComparable<T>
    { if (a.CompareTo(b) == 1) { a = b; return true; } return false; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static bool chmax<T>(ref T a, T b) where T : IComparable<T>
    { if (a.CompareTo(b) == -1) { a = b; return true; } return false; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static void swap<T>(ref T a, ref T b)
    { var t = b; b = a; a = t; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T[] Create<T>(int n, Func<T> f) { var rt = new T[n]; for (var i = 0; i < rt.Length; ++i) rt[i] = f(); return rt; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T[] Create<T>(int n, Func<int, T> f) { var rt = new T[n]; for (var i = 0; i < rt.Length; ++i) rt[i] = f(i); return rt; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T[] Copy<T>(this T[] A) => Create(A.Length, i => A[i]);
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static Pair<T, U> MP<T, U>(T t, U u) => new Pair<T, U>(t, u);
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static Pair<T, U, V> MP<T, U, V>(T t, U u, V v) => new Pair<T, U, V>(t, u, v);
    public static void Fail<T>(T s) { Console.WriteLine(s); Console.Out.Close(); Environment.Exit(0); }
}

public class Scanner
{
    public string Str => Console.ReadLine().Trim();
    public int Int => int.Parse(Str);
    public long Long => long.Parse(Str);
    public double Double => double.Parse(Str);
    public int[] ArrInt => Str.Split(' ').Select(int.Parse).ToArray();
    public long[] ArrLong => Str.Split(' ').Select(long.Parse).ToArray();
    public char[][] Grid(int n) => Create(n, () => Str.ToCharArray());
    public int[] ArrInt1D(int n) => Create(n, () => Int);
    public long[] ArrLong1D(int n) => Create(n, () => Long);
    public int[][] ArrInt2D(int n) => Create(n, () => ArrInt);
    public long[][] ArrLong2D(int n) => Create(n, () => ArrLong);
    public Pair<T1, T2> MP<T1, T2>() => new Pair<T1, T2>(Next<T1>(), Next<T2>());
    public Pair<T1, T2, T3> MP<T1, T2, T3>() => new Pair<T1, T2, T3>(Next<T1>(), Next<T2>(), Next<T3>());
    private Queue<string> q = new Queue<string>();
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public T Next<T>() { if (q.Count == 0) foreach (var item in Str.Split(' ')) q.Enqueue(item); return (T)Convert.ChangeType(q.Dequeue(), typeof(T)); }
    public void Make<T1>(out T1 v1) => v1 = Next<T1>();
    public void Make<T1, T2>(out T1 v1, out T2 v2) { v1 = Next<T1>(); v2 = Next<T2>(); }
    public void Make<T1, T2, T3>(out T1 v1, out T2 v2, out T3 v3) { Make(out v1, out v2); v3 = Next<T3>(); }
    public void Make<T1, T2, T3, T4>(out T1 v1, out T2 v2, out T3 v3, out T4 v4) { Make(out v1, out v2, out v3); v4 = Next<T4>(); }
    public void Make<T1, T2, T3, T4, T5>(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5) { Make(out v1, out v2, out v3, out v4); v5 = Next<T5>(); }
    public void Make<T1, T2, T3, T4, T5, T6>(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6) { Make(out v1, out v2, out v3, out v4, out v5); v6 = Next<T6>(); }
}

public class Pair<T1, T2> : IComparable<Pair<T1, T2>>
{
    public T1 v1;
    public T2 v2;
    public Pair() { }
    public Pair(T1 v1, T2 v2)
    { this.v1 = v1; this.v2 = v2; }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public int CompareTo(Pair<T1, T2> p)
    {
        var c = Comparer<T1>.Default.Compare(v1, p.v1);
        if (c == 0)
            c = Comparer<T2>.Default.Compare(v2, p.v2);
        return c;
    }
    public override string ToString() => $"{v1.ToString()} {v2.ToString()}";
    public void Tie(out T1 a, out T2 b) { a = v1; b = v2; }
}

public class Pair<T1, T2, T3> : Pair<T1, T2>, IComparable<Pair<T1, T2, T3>>
{
    public T3 v3;
    public Pair() : base() { }
    public Pair(T1 v1, T2 v2, T3 v3) : base(v1, v2)
    { this.v3 = v3; }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public int CompareTo(Pair<T1, T2, T3> p)
    {
        var c = base.CompareTo(p);
        if (c == 0)
            c = Comparer<T3>.Default.Compare(v3, p.v3);
        return c;
    }
    public override string ToString() => $"{base.ToString()} {v3.ToString()}";
    public void Tie(out T1 a, out T2 b, out T3 c) { Tie(out a, out b); c = v3; }
}
#endregion


Measured memory_bytes: 31884