#region いつもの
#pragma warning disable
using System;
using System.Collections.Generic;
using System.Linq;
using IEnumerable = System.Collections.IEnumerable;
using IEnumerator = System.Collections.IEnumerator;
using BitArray = System.Collections.BitArray;
using BigInteger = System.Numerics.BigInteger;
using TextReader = System.IO.TextReader;
using static Global;
using static NumGlobal;

static class Global
{
    private class ComparerReverseImpl<T> : Comparer<T> where T : IComparable<T> { public override int Compare(T y, T x) => x.CompareTo(y); public override bool Equals(object obj) => obj != null && GetType() == obj.GetType(); public override int GetHashCode() => GetType().GetHashCode(); }
    public static IComparer<T> ComparerReverse<T>() where T : IComparable<T> => new ComparerReverseImpl<T>();
    public static string AllLines<T>(IEnumerable<T> source) => string.Join("\n", source);
    public static string AllJoin<T>(IEnumerable<T> source) => string.Join(" ", source);
}
static class NumGlobal
{
    public static BigInteger ParseBigInteger(string s)
    {
        // MonoのBigInteger.Parseが遅いので自前実装
        var res = BigInteger.Zero;
        var splited = new string[(s.Length + 7) / 8];
        for (var i = 0; i < splited.Length - 1; i++)
        {
            splited[i] = s.Substring(8 * i, 8);
        }
        splited[splited.Length - 1] = s.Substring(8 * (splited.Length - 1));
        foreach (var sp in splited)
        {
            res *= (int)Math.Pow(10, sp.Length);
            res += int.Parse(sp);
        }
        return res;
    }
    public static int BitCount(int x)
    {
        x = x - ((x >> 1) & 0x55555555);
        x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
        x = (x + (x >> 4)) & 0x0f0f0f0f;
        x = x + (x >> 8);
        x = x + (x >> 16);
        return x & 0x3f;
    }
    public static int BitCount(long x)
    {
        x = x - ((x >> 1) & 0x5555555555555555);
        x = (x & 0x3333333333333333) + ((x >> 2) & 0x3333333333333333);
        x = (x + (x >> 4)) & 0x0f0f0f0f0f0f0f0f;
        x = x + (x >> 8);
        x = x + (x >> 16);
        x = x + (x >> 32);
        return (int)(x & 0x0000007f);
    }
    public static int MSB(int x)
    {
        x |= (x >> 1);
        x |= (x >> 2);
        x |= (x >> 4);
        x |= (x >> 8);
        x |= (x >> 16);
        return BitCount(x) - 1;
    }
    public static int MSB(long x)
    {
        x |= (x >> 1);
        x |= (x >> 2);
        x |= (x >> 4);
        x |= (x >> 8);
        x |= (x >> 16);
        x |= (x >> 32);
        return BitCount(x) - 1;
    }
    public static int LSB(int x)
    {
        x |= (x << 1);
        x |= (x << 2);
        x |= (x << 4);
        x |= (x << 8);
        x |= (x << 16);
        return 32 - BitCount(x);
    }
    public static int LSB(long x)
    {
        x |= (x << 1);
        x |= (x << 2);
        x |= (x << 4);
        x |= (x << 8);
        x |= (x << 16);
        x |= (x << 32);
        return 64 - BitCount(x);
    }
}
static class Ext
{
    public static T[] Sort<T>(this T[] arr)
    {
        Array.Sort(arr);
        return arr;
    }
    public static T[] Reverse<T>(this T[] arr)
    {
        Array.Reverse(arr);
        return arr;
    }
    public static T[][] Chunk<T>(this T[,] source)
    {
        var len0 = source.GetLength(0);
        var len1 = source.GetLength(1);
        var res = new T[len0][];
        for (var i = 0; i < len0; i++)
        {
            res[i] = new T[len1];
            for (var j = 0; j < len1; j++)
            {
                res[i][j] = source[i, j];
            }
        }
        return res;
    }

    public static Tuple<TSource, TMax> MaxBy<TSource, TMax>
        (this IEnumerable<TSource> source, Func<TSource, TMax> maxBySelector)
        where TMax : IComparable<TMax>
    {
        TMax max;
        TSource maxByItem;

        var e = source.GetEnumerator();
        e.MoveNext();
        maxByItem = e.Current;
        max = maxBySelector(maxByItem);
        while (e.MoveNext())
        {
            var item = e.Current;
            var next = maxBySelector(item);
            if (max.CompareTo(next) < 0)
            {
                max = next;
                maxByItem = item;
            }
        }
        return Tuple.Create(maxByItem, max);
    }
    public static Tuple<TSource, TMin> MinBy<TSource, TMin>
        (this IEnumerable<TSource> source, Func<TSource, TMin> minBySelector)
        where TMin : IComparable<TMin>
    {
        TMin min;
        TSource minByItem;

        var e = source.GetEnumerator();
        e.MoveNext();
        minByItem = e.Current;
        min = minBySelector(minByItem);
        while (e.MoveNext())
        {
            var item = e.Current;
            var next = minBySelector(item);
            if (min.CompareTo(next) > 0)
            {
                min = next;
                minByItem = item;
            }
        }
        return Tuple.Create(minByItem, min);
    }
    public static IComparer<T> Reverse<T>(this IComparer<T> comparer) => Comparer<T>.Create((x, y) => comparer.Compare(y, x));
    public static Dictionary<TKey, int> GroupCount<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector) => source.GroupBy(keySelector).ToDictionary(g => g.Key, g => g.Count());
    public static Dictionary<TKey, int> GroupCount<TKey>(this IEnumerable<TKey> source) => source.GroupCount(i => i);
}
public class ConsoleReader { private string[] ReadLineSplit() => textReader.ReadLine().Split(Array.Empty<char>(), StringSplitOptions.RemoveEmptyEntries); private string[] line = Array.Empty<string>(); private int linePosition; private TextReader textReader; public ConsoleReader(TextReader tr) { textReader = tr; } public int Int => int.Parse(String); public int Int0 => Int - 1; public long Long => long.Parse(String); public double Double => double.Parse(String); public string String { get { if (linePosition >= line.Length) { linePosition = 0; line = ReadLineSplit(); } return line[linePosition++]; } } public class SplitLine { private string[] splited; public SplitLine(ConsoleReader cr) { splited = cr.ReadLineSplit(); cr.line = Array.Empty<string>(); } public int[] Int => String.Select(x => int.Parse(x)).ToArray(); public int[] Int0 => String.Select(x => int.Parse(x) - 1).ToArray(); public long[] Long => String.Select(x => long.Parse(x)).ToArray(); public double[] Double => String.Select(x => double.Parse(x)).ToArray(); public string[] String => splited; } public SplitLine Split => new SplitLine(this); public class RepeatReader : IEnumerable<ConsoleReader> { ConsoleReader cr; int count; public RepeatReader(ConsoleReader cr, int count) { this.cr = cr; this.count = count; } public IEnumerator<ConsoleReader> GetEnumerator() => Enumerable.Repeat(cr, count).GetEnumerator(); System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => GetEnumerator(); public string[] String => this.Select(cr => cr.String).ToArray(); public int[] Int => this.Select(cr => cr.Int).ToArray(); public int[] Int0 => this.Select(cr => cr.Int - 1).ToArray(); public long[] Long => this.Select(cr => cr.Long).ToArray(); public double[] Double => this.Select(cr => cr.Double).ToArray(); } public RepeatReader Repeat(int count) => new RepeatReader(this, count); }
public class Program
{
    [System.Diagnostics.DebuggerBrowsable(System.Diagnostics.DebuggerBrowsableState.Never)] private ConsoleReader cr;
    public Program(ConsoleReader consoleReader) { this.cr = consoleReader; }
    static void Main() => Console.WriteLine(new Program(new ConsoleReader(Console.In)).Calc());

    #endregion
    public object Calc()
    {
        var N = cr.Int;
        var D = cr.Long;
        var A = cr.Long;

        var monsters = new Monster[N];
        for (int i = 0; i < N; i++)
        {
            monsters[i] = new Monster { x = cr.Long, hp = cr.Long };
        }

        Array.Sort(monsters, (m1, m2) => m1.x.CompareTo(m2.x));

        var bit = new BinaryIndexedTree(N);
        long cnt = 0;
        int l = 0;
        for (int i = 0; i < N; i++)
        {
            while (monsters[l].x + 2 * D < monsters[i].x) l++;
            var hp = monsters[i].hp - bit.Sum(l, i + 1);
            if (hp <= 0) continue;
            var c = (hp + A - 1) / A;
            bit.Add(i, A * c);
            cnt += c;
        }

        return cnt;
    }
}
struct Monster
{
    public long x;
    public long hp;
}
class BinaryIndexedTree
{
    public void Add(int i, long w)
    {
        for (++i; i < tree.Length; i += (i & -i))
            tree[i] += w;
    }
    public long Sum(int toExclusive)
    {
        long res = 0;
        for (var i = toExclusive; i > 0; i -= (i & -i))
            res += tree[i];
        return res;
    }
    public long Sum(int from, int toExclusive) => Sum(toExclusive) - Sum(from);

    private long[] tree;

    public BinaryIndexedTree(int size)
    {
        tree = new long[size + 1];
    }

    public class BinaryIndexedTreeDebugView
    {
        private BinaryIndexedTree bit;
        public BinaryIndexedTreeDebugView(BinaryIndexedTree bit)
        {
            this.bit = bit;
        }

        [System.Diagnostics.DebuggerBrowsable(System.Diagnostics.DebuggerBrowsableState.RootHidden)]
        public string[] Tree
        {
            get
            {
                var res = new string[bit.tree.Length - 1];
                for (var i = 0; i < res.Length; i++)
                {
                    res[i] = $"real:{bit.tree[i + 1]} num:{bit.Sum(i, i + 1)}";
                }
                return res;
            }
        }
    }
}


Measured memory_bytes: 19876