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 Rust (1.15.1) (judge verdict: Runtime Error)

// use std::io::stdin;

fn main() {
    let vec: Vec<i32> = get_input_by_vec();
    // 0: N 体のモンスター
    // 1: D 爆弾の範囲
    // 2: A 爆弾のダメージ
    let (mut each_hp_and_location, vector_size) = get_input_by_loop(vec[0]);
    let mut monster_location_and_hp = vec![0; vector_size + 1];
    let (mut _location, mut _hp) = (0, 0);
    let mut locations = Vec::new();
    for _i in 0..vec[0] {
        // println!("{}",i );
        _hp = each_hp_and_location.pop().unwrap();
        _location = each_hp_and_location.pop().unwrap();
        // println!("location: {}, hp: {}",location, hp );
        monster_location_and_hp[_location as usize] = _hp;
        locations.push(_location);
    }

    // print!("[");
    // for i in &monster_location_and_hp {
    //     print!("{}, ",i );
    // }
    // println!("]");

    locations.sort();
    let mut used_bomb: i64 = 0;
    let bomb_range = vec[1] * 2;
    let damage = vec[2];
    // let mut counter = 0;
    let mut _using_bomb_position = vector_size; // 暫定値

    while  locations.len() > 0 {
        // counter += 1;
        // println!("count {}",counter );

        // モンスターの位置を取得
        let next_monster_location = locations.pop().unwrap();

        //if // HP==0(前のBombで死んだとき）の時はcontinue
        if monster_location_and_hp[next_monster_location as usize] <= 0 {continue;}

        // BOMBダメージ計算（対象のモンスター）
        // 累積（巻き添え）ダメージを初期化
        let mut _accumulation_damage = 0;

        // BOM位置が範囲を外れた時はBOMの範囲で使用
        if next_monster_location - (bomb_range / 2) < 0 {_using_bomb_position = 0}

        //累積カウントの計算（Temp）
        _accumulation_damage = (monster_location_and_hp[next_monster_location as usize] + damage - 1) / damage;

        // 使用回数を計算
        used_bomb += _accumulation_damage as i64;

        _accumulation_damage *= damage;

        // println!("  accumulation:{}",accumulation_damage );
        // println!("  next_monster_location: {}", next_monster_location);
        // BOMBダメージ計算（対象のモンスター）
        for i in 0..(bomb_range + 1) {

            // 範囲外に出たら終了
            if next_monster_location < i {break;}

            // bom positionの変更
            let position = (next_monster_location -i) as usize;
            // println!("target: {}",position );

            // 巻き添えダメージの計算
            monster_location_and_hp[position] -= _accumulation_damage;

            // 累積ダメージで、またはもともといない時は次のループに
            if monster_location_and_hp[position] <= 0 {continue;}
        }
    }
    println!("{}",used_bomb);
}


fn get_input_by_vec() -> Vec<i32> {
    let mut input  = String::new();
    std::io::stdin().read_line(&mut input).unwrap();
    let mut _vec: Vec<i32> = input.split_whitespace()
                            .map(|x| x.parse().unwrap())
                            .collect();
    _vec
}

fn get_input_by_loop(loop_count: i32) -> (Vec<i32>, usize) {
    let mut input = String::new();
    let mut max = 0;
    let mut temp = 0;
    for _i in 0..loop_count {
        std::io::stdin().read_line(&mut input).unwrap();
    }
    (input.split_whitespace()
         .map(|x| {
             temp = x.parse::<i32>().unwrap();
             if temp > max {max = temp;}
             x.parse::<i32>().unwrap()
         })
         .collect()
    , max as usize)
}