Problem:
Score : 600 points

Problem Statement

Silver Fox is fighting with N monsters.

The monsters are standing in a row, and we can assume them to be standing on a number line. The i-th monster, standing at the coordinate X_i, has the health of H_i.

Silver Fox can use bombs to attack the monsters.
Using a bomb at the coordinate x decreases the healths of all monsters between the coordinates x-D and x+D (inclusive) by A.
There is no way other than bombs to decrease the monster's health.

Silver Fox wins when all the monsters' healths become 0 or below.

Find the minimum number of bombs needed to win.

Constraints

1 \leq N \leq 2 \times 10^5

0 \leq D \leq 10^9

1 \leq A \leq 10^9

0 \leq X_i \leq 10^9

1 \leq H_i \leq 10^9

X_i are distinct.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N D A
X_1 H_1
:
X_N H_N

Output

Print the minimum number of bombs needed to win.

Sample Input 1

3 3 2
1 2
5 4
9 2

Sample Output 1

2

First, let us use a bomb at the coordinate 4 to decrease the first and second monsters' health by 2.

Then, use a bomb at the coordinate 6 to decrease the second and third monsters' health by 2.

Now, all the monsters' healths are 0.
We cannot make all the monsters' health drop to 0 or below with just one bomb.

Sample Input 2

9 4 1
1 5
2 4
3 3
4 2
5 1
6 2
7 3
8 4
9 5

Sample Output 2

5

We should use five bombs at the coordinate 5.

Sample Input 3

3 0 1
300000000 1000000000
100000000 1000000000
200000000 1000000000

Sample Output 3

3000000000

Watch out for overflow.

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Text;
using System.Collections.Generic;
using System.Collections;
using static System.Math;
using System.Linq;
using static System.Array;

namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {
            //var N = long.Parse(Console.ReadLine());
            Solve();

        }
        static void Solve()
        {
            var inp = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
            var N = inp[0];
            var D = inp[1];
            var A = inp[2];
            var Monster = new Tuple<long, long>[N];
            for (int i = 0; i < N; i++)
            {
                var XH = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
                Monster[i] = new Tuple<long, long>(XH[0], XH[1]);
            }
            Sort(Monster);
            var que = new Queue<long>();
            long CumlatedDamage = 0;
            que.Enqueue(Monster[0].Item2);
            long MaxRange = Monster[0].Item1 + 2 * D;
            long TopNum = 0;
            long TargetMonsterSum = 1;
            long ans = 0;
            while (TopNum < N)
            {
                MaxRange = Monster[TopNum].Item1 + 2 * D;
                while (TargetMonsterSum < N && Monster[TargetMonsterSum].Item1 <= MaxRange)
                {
                    que.Enqueue(Monster[TargetMonsterSum].Item2 + CumlatedDamage);
                    TargetMonsterSum++;
                }
                var tmp = ((que.Peek() - CumlatedDamage - 1) / A) + 1;
                ans += tmp;
                CumlatedDamage += tmp * A;

                while(que.Count >0 && que.Peek() <= CumlatedDamage)
                {
                    que.Dequeue();
                    TopNum++;
                }
                
            }

            Console.WriteLine(ans);
        }
    }

}