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: Wrong Answer)

fn main() {
    let (n, d, a): (usize, usize, usize) = {
        let mut i = String::new();
        std::io::stdin().read_line(&mut i).unwrap();
        let mut it = i.split_whitespace();
        (
            it.next().unwrap().parse().unwrap(),
            it.next().unwrap().parse().unwrap(),
            it.next().unwrap().parse().unwrap(),
        )
    };
    let mut monsters = Vec::<(usize, usize)>::new();
    for _ in 1..n {
        let mut i = String::new();
        std::io::stdin().read_line(&mut i).unwrap();
        let mut it = i.split_whitespace();
        monsters.push((
            it.next().unwrap().parse::<usize>().unwrap(),
            it.next().unwrap().parse::<usize>().unwrap(),
        ));
    }
    monsters.sort();
    // for &(x, h) in &monsters {
    //     println!("x:{},h:{}", x, h)
    // }
    let mut ans: usize = 0;
    for i in 0..monsters.len() {
        let (x, h) = monsters[i];
        if h != 0 {
            let times_now: usize = h / a;
            //println!("x:{},h:{},攻撃{}回", x, h, times_now);
            ans += times_now;
            for j in i + 1..monsters.len() {
                if monsters[j].0 >= x && monsters[j].0 <= x + 2 * d {
                    if monsters[j].1 <= times_now * a {
                        monsters[j].1 = 0;
                    } else {
                        monsters[j].1 -= times_now * a;
                    }
                }
            }
        }
    }
    println!("{}", ans);
}