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: Accepted)

//  ____            _                  _                       _       _
// |  _ \ _   _ ___| |_    ___ _ __   | |_ ___ _ __ ___  _ __ | | __ _| |_ ___
// | |_) | | | / __| __|  / __| '_ \  | __/ _ \ '_ ` _ \| '_ \| |/ _` | __/ _ \
// |  _ <| |_| \__ \ |_  | (__| |_) | | ||  __/ | | | | | |_) | | (_| | ||  __/
// |_| \_\\__,_|___/\__|  \___| .__/___\__\___|_| |_| |_| .__/|_|\__,_|\__\___|
//                            |_| |_____|               |_|

//https://github.com/manta1130/Competitive_Programming_Template_Rust

#[macro_use]
mod input {

    use std;
    use std::io;

    const SPLIT_DELIMITER: char = ' ';

    #[macro_export]
    #[allow(unused_macros)]
    macro_rules! input {
    ( $($x:expr ),*) => {
        {
            let temp_str = input_line_str();
            let mut split_result_iter = temp_str.split_whitespace();
                $(
                let buf_split_result = split_result_iter.next();
                let buf_split_result = buf_split_result.unwrap();
                    ($x) = buf_split_result.parse().unwrap();
                )*
        }
    };
}

    #[allow(dead_code)]
    pub fn input_line_str() -> String {
        let mut s = String::new();
        io::stdin().read_line(&mut s).unwrap();
        s.trim().to_string()
    }

    #[allow(dead_code)]
    pub fn p<T>(t: T)
    where
        T: std::fmt::Display,
    {
        println!("{}", t);
    }

    #[allow(dead_code)]
    pub fn input_vector2d<T>(line: usize) -> Vec<Vec<T>>
    where
        T: std::str::FromStr,
    {
        let mut v: Vec<Vec<T>> = Vec::new();

        for _ in 0..line {
            let vec_line = input_vector();
            v.push(vec_line);
        }
        v
    }

    #[allow(dead_code)]
    pub fn input_vector<T>() -> Vec<T>
    where
        T: std::str::FromStr,
    {
        let mut v: Vec<T> = Vec::new();

        let s = input_line_str();
        let split_result = s.split(SPLIT_DELIMITER);
        for z in split_result {
            let buf = match z.parse() {
                Ok(r) => r,
                Err(_) => panic!("Parse Error"),
            };
            v.push(buf);
        }
        v
    }

    #[allow(dead_code)]
    pub fn input_vector_row<T>(n: usize) -> Vec<T>
    where
        T: std::str::FromStr,
    {
        let mut v = Vec::with_capacity(n);
        for _ in 0..n {
            let buf = match input_line_str().parse() {
                Ok(r) => r,
                Err(_) => panic!("Parse Error"),
            };
            v.push(buf);
        }
        v
    }

    pub trait ToCharVec {
        fn to_charvec(&self) -> Vec<char>;
    }

    impl ToCharVec for String {
        fn to_charvec(&self) -> Vec<char> {
            self.to_string().chars().collect::<Vec<_>>()
        }
    }
}

mod vectools {

///C++のupper_boundと同等の実装
pub fn upper_bound<T>(v: &Vec<T>, k: T) -> usize
where
    T: PartialOrd,
{
    let mut from = 0;
    let mut to = v.len();

    while to - from > 1 {
        let mid = (from + to) / 2;
        if v[mid] <= k {
            from = mid;
        } else {
            to = mid;
        }
    }
    if v[from] > k {
        from
    } else {
        to
    }
}

///C++のlower_boundと同等の実装
pub fn lower_bound<T>(v: &Vec<T>, k: T) -> usize
where
    T: PartialOrd,
{
    let mut from = 0;
    let mut to = v.len();

    while to - from > 1 {
        let mid = (from + to) / 2;
        if v[mid] < k {
            from = mid;
        } else {
            to = mid;
        }
    }

    if v[from] < k {
        to
    } else {
        from
    }
}

///次の順列を求める。
pub fn next_permutation<T>(v: &mut Vec<T>) -> bool
where
    T: PartialOrd,
{
    let mut pivot = v.len() - 1;
    loop {
        if pivot == 0 {
            return false;
        }
        if v[pivot] > v[pivot - 1] {
            pivot -= 1;
            break;
        }
        pivot -= 1;
    }
    let mut pivot_swap = v.len() - 1;
    while v[pivot] >= v[pivot_swap] {
        pivot_swap -= 1;
    }
    v.swap(pivot, pivot_swap);
    v[pivot + 1..].reverse();
    true
}

}

use input::*;
use vectools::*;

fn main() {
    let (n, d, a): (usize, usize, isize);
    input!(n, d, a);
    let mut v = vec![];
    for i in 0..n {
        let (x, h): (usize, isize);
        input!(x, h);
        v.push((x, h))
    }
    let block_size = (v.len() as f64).sqrt() as usize;
    let mut block = vec![0; block_size + 10];
    v.sort();
    let mut x = vec![];
    let mut h = vec![];
    for i in 0..v.len() {
        x.push(v[i].0);
        h.push(v[i].1);
    }

    let mut ans = 0;
    for i in 0..n {
        if h[i] - block[i / block_size] <= 0{
            continue;
        }
        let lp = if (h[i] - block[i / block_size]) % a == 0 {
            (h[i] - block[i / block_size]) / a
        } else {
            ((h[i] - block[i / block_size]) / a) + 1
        };
        let now = x[i];
        let z = upper_bound(&x, now + 2 * d);

        let mut j = i;
        ans += lp;
        while j < z {
            if j % block_size == 0 && j + block_size < z {
                block[j / block_size] += lp * a;
                j += block_size;
            } else {
                h[j] -= lp * a;
                j += 1;
            }
        }
    }
    println!("{}", ans);
}