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use std::io;
use std::io::Write;
use std::str;
use std::cmp::{max,min};

/// https://github.com/EbTech/rust-algorithms/blob/master/src/scanner.rs
pub struct Scanner<R> {
    reader: R,
    buffer: Vec<String>,
}

impl<R: io::BufRead> Scanner<R> {
    pub fn new(reader: R) -> Self {
        Self {
            reader,
            buffer: vec![],
        }
    }

    pub fn token<T: str::FromStr>(&mut self) -> T {
        loop {
            if let Some(token) = self.buffer.pop() {
                return token.parse().ok().expect("Failed parse");
            }
            let mut input = String::new();
            self.reader.read_line(&mut input).expect("Failed read");
            self.buffer = input.split_whitespace().rev().map(String::from).collect();
        }
    }
}

fn main() {
    let mut scan = Scanner::new(io::stdin().lock());

    let n = scan.token::<usize>();
    let k = scan.token::<i64>();
    
    let tab: Vec<i64> = (0..n).map(|_| scan.token()).collect();
    let mut copy = tab.clone();
    let mut sorted = tab.iter().cloned().enumerate().collect::<Vec<_>>();

    sorted.sort_by_key(|x| -x.1);
  
    for (i, _) in sorted {
        for j in i+1..n {
            copy[j] = max(copy[j], copy[j-1]-k);
        }
        for j in (0..i).rev() {
            copy[j] = max(copy[j], copy[j+1]-k);
        }
    }
    println!("{}", tab.into_iter().zip(copy).map(|(a,b)| b-a).sum::<i64>());
}