use std::io;

fn main() {
    let mut s = String::new();
    io::stdin().read_line(&mut s).unwrap();
    let b: Vec<usize> = s.split_whitespace().
        map(|x| x.parse().unwrap()).
        collect();
    let n: usize = b[0];
    let k: usize = b[1];
    s.clear();
    io::stdin().read_line(&mut s).unwrap();
    let mut a: Vec<usize> = s.split_whitespace().
        map(|x| x.parse().unwrap()).
        collect();
    let mut ans = 0;
    for i in 1..n {
        if a[i] > a[i - 1] {
            if a[i] > a[i - 1] + k {
                for j in (0..i).rev() {
                    if a[j + 1] > a[j] + k {
                        ans += a[j + 1] - a[j] - k;
                        a[j] = a[j + 1] - k;
                    }
                }
            }
        } else {
            if a[i - 1] > a[i] + k {
                ans += a[i - 1] - a[i] - k;
                a[i] = a[i -  1] - k;
            }
        }
    }
    println!("{}", ans);
}