using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using System.Runtime.CompilerServices;

namespace FertiLib.Contest.F
{
	static class Program
	{
		public static void Solve(Scanner cin)
		{
			var (n, d, a) = cin.ReadValue<int, long, long>();
			var (x, h) = cin.ReadValueArray<long, long>(n);
			var l = new List<Pair<long, long>>();
			for (int i = 0; i < n; i++)
			{
				l.Add(new Pair<long, long>(x[i], h[i]));
			}
			l.Sort();
			Array.Sort(x);
			long ans = 0;
			int seen = 0;
			var segtree = new SegmentTree<long>(n, (x, y) => x + y, 0);
			while (seen < n)
			{
				var index = BinarySearch.LowerBound(x, l[seen].First - 2 * d);
				var decreased = segtree.GetResult(index, seen + 1);
				long t = Math.Max(0, (l[seen].Second - a * decreased + a - 1) / a);
				segtree.Update(seen, t);

				ans += t;

				seen++;
			}
			Console.WriteLine(ans);
		}

		public static void Main(string[] args)
		{
			var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
			Console.SetOut(sw);
			var cin = new Scanner();
			Solve(cin);
			Console.Out.Flush();
		}

		public static void YESNO(bool condition) => Console.WriteLine(condition ? "YES" : "NO");
		public static void YesNo(bool condition) => Console.WriteLine(condition ? "Yes" : "No");
		public static void yesno(bool condition) => Console.WriteLine(condition ? "yes" : "no");

		public static bool Chmax<T>(ref T a, T b) where T : IComparable<T>
		{
			if (a.CompareTo(b) >= 0) return false;
			a = b;
			return true;
		}
		public static bool Chmin<T>(ref T a, T b) where T : IComparable<T>
		{
			if (a.CompareTo(b) <= 0) return false;
			a = b;
			return true;
		}
	}

	static class BinarySearch
	{
		public static int UpperBound<T>(T[] array, T value) => UpperBound(array, 0, array.Length - 1, value, Comparer<T>.Default);

		public static int UpperBound<T>(T[] array, T value, Comparer<T> comparer) => UpperBound(array, 0, array.Length - 1, value, comparer);

		public static int UpperBound<T>(T[] array, int index, int length, T value) => UpperBound(array, index, length, value, Comparer<T>.Default);

		public static int UpperBound<T>(T[] array, int index, int length, T value, Comparer<T> comparer)
		{
			var l = index - 1;
			var r = index + length;
			while (r - l > 1)
			{
				var mid = l + (r - l) / 2;
				var res = comparer.Compare(array[mid], value);
				if (res <= 0) l = mid;
				else r = mid;
			}
			return r;
		}

		public static int UpperBound<T>(this List<T> list, T item) => list.UpperBound(0, list.Count, item, Comparer<T>.Default);

		public static int UpperBound<T>(this List<T> list, T item, Comparer<T> comparer) => list.UpperBound(0, list.Count, item, comparer);

		public static int UpperBound<T>(this List<T> list, int index, int count, T item, Comparer<T> comparer)
		{
			var l = index - 1;
			var r = index + count;
			while (r - l > 1)
			{
				var mid = l + (r - l) / 2;
				var res = comparer.Compare(list[mid], item);
				if (res <= 0) l = mid;
				else r = mid;
			}
			return r;
		}

		public static int LowerBound<T>(T[] array, T value) => LowerBound(array, 0, array.Length - 1, value, Comparer<T>.Default);

		public static int LowerBound<T>(T[] array, T value, Comparer<T> comparer) => LowerBound(array, 0, array.Length - 1, value, comparer);

		public static int LowerBound<T>(T[] array, int index, int length, T value) => LowerBound(array, index, length, value, Comparer<T>.Default);

		public static int LowerBound<T>(T[] array, int index, int length, T value, Comparer<T> comparer)
		{
			var l = index - 1;
			var r = index + length;
			while (r - l > 1)
			{
				var mid = l + (r - l) / 2;
				var res = comparer.Compare(array[mid], value);
				if (res == -1) l = mid;
				else r = mid;
			}
			return r;
		}

		public static int LowerBound<T>(this List<T> list, T item) => list.LowerBound(0, list.Count, item, Comparer<T>.Default);

		public static int LowerBound<T>(this List<T> list, T item, Comparer<T> comparer) => list.LowerBound(0, list.Count, item, comparer);

		public static int LowerBound<T>(this List<T> list, int index, int count, T item, Comparer<T> comparer)
		{
			var l = index - 1;
			var r = index + count;
			while (r - l > 1)
			{
				var mid = l + (r - l) / 2;
				var res = comparer.Compare(list[mid], item);
				if (res == -1) l = mid;
				else r = mid;
			}
			return r;
		}
	}

	public class Pair<T, U> : IComparable, IComparable<Pair<T, U>>, IEquatable<Pair<T, U>> where T : IComparable<T>, IEquatable<T> where U : IComparable<U>, IEquatable<U>
	{
		public T First { get; set; }
		public U Second { get; set; }

		public Pair(T first, U second)
		{
			First = first;
			Second = second;
		}

		public int CompareTo(object obj)
		{
			Pair<T, U> castedObj = (Pair<T, U>)obj;
			int x = First.CompareTo(castedObj.First);
			if (x != 0) return x;
			else return Second.CompareTo(castedObj.Second);
		}

		public int CompareTo(Pair<T, U> x)
		{
			int t = First.CompareTo(x.First);
			if (t != 0) return t;
			else return Second.CompareTo(x.Second);
		}

		public static bool operator ==(Pair<T, U> x, Pair<T, U> y) => x.CompareTo(y) == 0;

		public static bool operator !=(Pair<T, U> x, Pair<T, U> y) => x.CompareTo(y) != 0;

		public static bool operator <(Pair<T, U> x, Pair<T, U> y) => x.CompareTo(y) == 1;

		public static bool operator >(Pair<T, U> x, Pair<T, U> y) => x.CompareTo(y) == -1;

		public static bool operator <=(Pair<T, U> x, Pair<T, U> y) => x.CompareTo(y) > 0;

		public static bool operator >=(Pair<T, U> x, Pair<T, U> y) => x.CompareTo(y) < 0;

		public override string ToString()
		{
			return $"{First}, {Second}";
		}

		public bool Equals(Pair<T, U> x) => First.Equals(x.First) && Second.Equals(x.Second);

		public override bool Equals(object obj)
		{
			return obj is Pair<T, U> pair &&
				   EqualityComparer<T>.Default.Equals(First, pair.First) &&
				   EqualityComparer<U>.Default.Equals(Second, pair.Second);
		}

		public override int GetHashCode()
		{
			unchecked
			{
				var hashCode = 405212230;
				hashCode = hashCode * -1521134295 + EqualityComparer<T>.Default.GetHashCode(First);
				hashCode = hashCode * -1521134295 + EqualityComparer<U>.Default.GetHashCode(Second);
				return hashCode;
			}
		}
	}

	public class SegmentTree<T>
	{
		public int Count { get; private set; }
		T[] tree;
		readonly Func<T, T, T> func;
		readonly T init;

		public SegmentTree(int size, Func<T, T, T> func, T init)
		{
			int n = 1;
			while (n <= size)
			{
				n *= 2;
			}
			Count = n;

			tree = Enumerable.Repeat(init, 2 * n - 1).ToArray();

			this.func = func;
			this.init = init;
		}

		public SegmentTree(IEnumerable<T> items, Func<T, T, T> func, T init) : this(items.Count(), func, init)
		{
			var array = items.ToArray();

			for (int i = 0; i < array.Length; i++)
			{
				tree[i + Count - 1] = array[i];
			}
			UpdateAll();
		}

		public T this[int index]
		{
			get => this.tree[index + Count - 1];
			private set => this.tree[index + Count - 1] = value;
		}

		public void Update(int index, T value)
		{
			index += Count - 1;
			tree[index] = value;
			while (index > 0)
			{
				index = (index - 1) / 2;
				tree[index] = func(tree[index * 2 + 1], tree[index * 2 + 2]);
			}
		}

		void UpdateAll()
		{
			int n = Count / 2;
			while (n > 0)
			{
				for (int i = 0; i < n; i++)
				{
					tree[n - 1 + i] = func(tree[2 * (n - 1 + i) + 1], tree[2 * (n - 1 + i) + 2]);
				}
				n /= 2;
			}
		}

		// Attention: [l, r). This result does not include r-th item.
		public T GetResult(int l, int r) => GetResult(l, r, 0, 0, Count);

		T GetResult(int l, int r, int k, int a, int b)
		{
			if (b <= l || r <= a) return init;
			if (l <= a && b <= r) return tree[k];

			var vl = GetResult(l, r, 2 * k + 1, a, (a + b) / 2);
			var vr = GetResult(l, r, 2 * k + 2, (a + b) / 2, b);

			return func(vl, vr);
		}
	}

	static class Util
	{
		public static string Join<T>(this IEnumerable<T> x, string separator = "") => string.Join(separator, x);
	}

	class Scanner
	{
		string[] s;
		int i;

		char[] separator = new char[] { ' ' };

		public Scanner()
		{
			s = new string[0];
			i = 0;
		}

		public string Read() => ReadString();

		public string ReadString()
		{
			if (i < s.Length) return s[i++];
			string st = Console.ReadLine();
			while (st == "") st = Console.ReadLine();
			s = st.Split(separator, StringSplitOptions.RemoveEmptyEntries);
			if (s.Length == 0) return ReadString();
			i = 0;
			return s[i++];
		}

		public string[] ReadStringArray(int N)
		{
			string[] Array = new string[N];
			for (int i = 0; i < N; i++)
			{
				Array[i] = ReadString();
			}
			return Array;
		}

		public int ReadInt()
		{
			return int.Parse(ReadString());
		}

		public int[] ReadIntArray(int N, int add = 0)
		{
			int[] Array = new int[N];
			for (int i = 0; i < N; i++)
			{
				Array[i] = ReadInt() + add;
			}
			return Array;
		}

		public long ReadLong()
		{
			return long.Parse(ReadString());
		}

		public long[] ReadLongArray(int N, long add = 0)
		{
			long[] Array = new long[N];
			for (int i = 0; i < N; i++)
			{
				Array[i] = ReadLong() + add;
			}
			return Array;
		}

		public double ReadDouble()
		{
			return double.Parse(ReadString());
		}

		public double[] ReadDoubleArray(int N, double add = 0)
		{
			double[] Array = new double[N];
			for (int i = 0; i < N; i++)
			{
				Array[i] = ReadDouble() + add;
			}
			return Array;
		}

		public T1 ReadValue<T1>() => (T1)Convert.ChangeType(ReadString(), typeof(T1));

		public (T1, T2) ReadValue<T1, T2>()
		{
			var inputs = ReadStringArray(2);
			var v1 = (T1)Convert.ChangeType(inputs[0], typeof(T1));
			var v2 = (T2)Convert.ChangeType(inputs[1], typeof(T2));
			return (v1, v2);
		}

		public (T1, T2, T3) ReadValue<T1, T2, T3>()
		{
			var inputs = ReadStringArray(3);
			var v1 = (T1)Convert.ChangeType(inputs[0], typeof(T1));
			var v2 = (T2)Convert.ChangeType(inputs[1], typeof(T2));
			var v3 = (T3)Convert.ChangeType(inputs[2], typeof(T3));
			return (v1, v2, v3);
		}

		public (T1, T2, T3, T4) ReadValue<T1, T2, T3, T4>()
		{
			var inputs = ReadStringArray(4);
			var v1 = (T1)Convert.ChangeType(inputs[0], typeof(T1));
			var v2 = (T2)Convert.ChangeType(inputs[1], typeof(T2));
			var v3 = (T3)Convert.ChangeType(inputs[2], typeof(T3));
			var v4 = (T4)Convert.ChangeType(inputs[3], typeof(T4));
			return (v1, v2, v3, v4);
		}

		public (T1, T2, T3, T4, T5) ReadValue<T1, T2, T3, T4, T5>()
		{
			var inputs = ReadStringArray(5);
			var v1 = (T1)Convert.ChangeType(inputs[0], typeof(T1));
			var v2 = (T2)Convert.ChangeType(inputs[1], typeof(T2));
			var v3 = (T3)Convert.ChangeType(inputs[2], typeof(T3));
			var v4 = (T4)Convert.ChangeType(inputs[3], typeof(T4));
			var v5 = (T5)Convert.ChangeType(inputs[4], typeof(T5));
			return (v1, v2, v3, v4, v5);
		}

		public (T1, T2, T3, T4, T5, T6) ReadValue<T1, T2, T3, T4, T5, T6>()
		{
			var inputs = ReadStringArray(6);
			var v1 = (T1)Convert.ChangeType(inputs[0], typeof(T1));
			var v2 = (T2)Convert.ChangeType(inputs[1], typeof(T2));
			var v3 = (T3)Convert.ChangeType(inputs[2], typeof(T3));
			var v4 = (T4)Convert.ChangeType(inputs[3], typeof(T4));
			var v5 = (T5)Convert.ChangeType(inputs[4], typeof(T5));
			var v6 = (T6)Convert.ChangeType(inputs[5], typeof(T6));
			return (v1, v2, v3, v4, v5, v6);
		}

		public (T1, T2, T3, T4, T5, T6, T7) ReadValue<T1, T2, T3, T4, T5, T6, T7>()
		{
			var inputs = ReadStringArray(7);
			var v1 = (T1)Convert.ChangeType(inputs[0], typeof(T1));
			var v2 = (T2)Convert.ChangeType(inputs[1], typeof(T2));
			var v3 = (T3)Convert.ChangeType(inputs[2], typeof(T3));
			var v4 = (T4)Convert.ChangeType(inputs[3], typeof(T4));
			var v5 = (T5)Convert.ChangeType(inputs[4], typeof(T5));
			var v6 = (T6)Convert.ChangeType(inputs[5], typeof(T6));
			var v7 = (T7)Convert.ChangeType(inputs[6], typeof(T7));
			return (v1, v2, v3, v4, v5, v6, v7);
		}

		public T1[] ReadValueArray<T1>(int N)
		{
			var v1 = new T1[N];
			for (int i = 0; i < N; i++)
			{
				v1[i] = ReadValue<T1>();
			}
			return v1;
		}

		public (T1[], T2[]) ReadValueArray<T1, T2>(int N)
		{
			var (v1, v2) = (new T1[N], new T2[N]);
			for (int i = 0; i < N; i++)
			{
				var (t1, t2) = ReadValue<T1, T2>();
				v1[i] = t1;
				v2[i] = t2;
			}
			return (v1, v2);
		}

		public (T1[], T2[], T3[]) ReadValueArray<T1, T2, T3>(int N)
		{
			var (v1, v2, v3) = (new T1[N], new T2[N], new T3[N]);
			for (int i = 0; i < N; i++)
			{
				var (t1, t2, t3) = ReadValue<T1, T2, T3>();
				v1[i] = t1;
				v2[i] = t2;
				v3[i] = t3;
			}
			return (v1, v2, v3);
		}

		public (T1[], T2[], T3[], T4[]) ReadValueArray<T1, T2, T3, T4>(int N)
		{
			var (v1, v2, v3, v4) = (new T1[N], new T2[N], new T3[N], new T4[N]);
			for (int i = 0; i < N; i++)
			{
				var (t1, t2, t3, t4) = ReadValue<T1, T2, T3, T4>();
				v1[i] = t1;
				v2[i] = t2;
				v3[i] = t3;
				v4[i] = t4;
			}
			return (v1, v2, v3, v4);
		}

		public (T1[], T2[], T3[], T4[], T5[]) ReadValueArray<T1, T2, T3, T4, T5>(int N)
		{
			var (v1, v2, v3, v4, v5) = (new T1[N], new T2[N], new T3[N], new T4[N], new T5[N]);
			for (int i = 0; i < N; i++)
			{
				var (t1, t2, t3, t4, t5) = ReadValue<T1, T2, T3, T4, T5>();
				v1[i] = t1;
				v2[i] = t2;
				v3[i] = t3;
				v4[i] = t4;
				v5[i] = t5;
			}
			return (v1, v2, v3, v4, v5);
		}

		public (T1[], T2[], T3[], T4[], T5[], T6[]) ReadValueArray<T1, T2, T3, T4, T5, T6>(int N)
		{
			var (v1, v2, v3, v4, v5, v6) = (new T1[N], new T2[N], new T3[N], new T4[N], new T5[N], new T6[N]);
			for (int i = 0; i < N; i++)
			{
				var (t1, t2, t3, t4, t5, t6) = ReadValue<T1, T2, T3, T4, T5, T6>();
				v1[i] = t1;
				v2[i] = t2;
				v3[i] = t3;
				v4[i] = t4;
				v5[i] = t5;
				v6[i] = t6;
			}
			return (v1, v2, v3, v4, v5, v6);
		}

		public (T1[], T2[], T3[], T4[], T5[], T6[], T7[]) ReadValueArray<T1, T2, T3, T4, T5, T6, T7>(int N)
		{
			var (v1, v2, v3, v4, v5, v6, v7) = (new T1[N], new T2[N], new T3[N], new T4[N], new T5[N], new T6[N], new T7[N]);
			for (int i = 0; i < N; i++)
			{
				var (t1, t2, t3, t4, t5, t6, t7) = ReadValue<T1, T2, T3, T4, T5, T6, T7>();
				v1[i] = t1;
				v2[i] = t2;
				v3[i] = t3;
				v4[i] = t4;
				v5[i] = t5;
				v6[i] = t6;
				v7[i] = t7;
			}
			return (v1, v2, v3, v4, v5, v6, v7);
		}
	}
}


Measured memory_bytes: 52080