Problem:
Score : 600 points

Problem Statement

There are N cities in Republic of AtCoder. The size of the i-th city is A_{i}.
Takahashi would like to build N-1 bidirectional roads connecting two cities so that any city can be reached from any other city by using these roads.

Assume that the cost of building a road connecting the i-th city and the j-th city is |i-j| \times D + A_{i} + A_{j}.
For Takahashi, find the minimum possible total cost to achieve the objective.

Constraints

1 \leq N \leq 2 \times 10^5

1 \leq D \leq 10^9

1 \leq A_{i} \leq 10^9

A_{i} and D are integers.

Input

Input is given from Standard Input in the following format:

N D
A_1 A_2 ... A_N

Output

Print the minimum possible total cost.

Sample Input 1

3 1
1 100 1

Sample Output 1

106

This cost can be achieved by, for example, building roads connecting City 1, 2 and City 1, 3.

Sample Input 2

3 1000
1 100 1

Sample Output 2

2202

Sample Input 3

6 14
25 171 7 1 17 162

Sample Output 3

497

Sample Input 4

12 5
43 94 27 3 69 99 56 25 8 15 46 8

Sample Output 4

658

Solution in Rust (1.15.1) (judge verdict: Accepted)

// ${url}
//
#![allow(unused_imports)]
use std::io::*;
use std::io::Write;
use std::fmt::*;
use std::str::*;
use std::cmp::*;
use std::collections::*;

#[allow(unused_macros)]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };

    ($iter:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, [ next / $t:tt ]) => {
        {
            let len = read_value!($iter, usize);
            (0..len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
        }
    };

    ($iter:expr, switch) => {
        {
            let ty = read_value!($iter, i32);
            if ty == 1 {
                vec![ty, read_value!($iter, i32), read_value!($iter, i32)]
            } else if ty == 2 {
                vec![ty, read_value!($iter, i32)]
            } else {
                vec![ty, read_value!($iter, i32)]
            }
        }
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

#[allow(unused_macros)]
macro_rules! dvec {
    ($t:expr ; $len:expr) => {
        vec![$t; $len]
    };

    ($t:expr ; $len:expr, $($rest:expr),*) => {
        vec![dvec!($t; $($rest),*); $len]
    };
}

#[allow(unused_macros)]
macro_rules! ifv {
    ($t:expr, $a:expr, $b: expr) => {
        if $t { $a } else { $b }
    }
}

#[allow(unused_macros)]
macro_rules! fill {
    ($t:expr, $v:expr) => {
        for i in 0..$t.len() {
            $t[i] = $v;
        }
    };
}

#[allow(unused_macros)]
macro_rules! join {
    ($t:expr, $glue:expr) => {
        $t.into_iter().map(|w| w.to_string()).collect::<Vec<_>>().join($glue)
    };
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
    }
}

// ===

// ====

use std::rc::Rc;
type Merger<T> = Rc<Fn(T, T) -> T>;

struct SegmentTree<T> {
    n: usize,
    default: T,
    bottom_offset: usize,
    data: Vec<T>,
    merger: Merger<T>,
}

impl<T: Debug + Copy + Eq> SegmentTree<T> {
    fn new(n: usize, initial: T, merger: Merger<T>) -> Self {
        let z = (8u32 * std::mem::size_of::<usize>() as u32) - n.leading_zeros();
        let size = (1<<z) as usize;
        SegmentTree {
            n: size*2,
            default: initial,
            bottom_offset: size,
            data: vec![initial; size*2],
            merger: merger,
        }
    }

    /// Change single position [i, i+1) to value v.
    fn set(&mut self, i: usize, v: T) {
        let mut idx = self.bottom_offset + i;
        self.data[idx] = v;
        while idx >= 1 {
            idx /= 2;
            self.data[idx] = (self.merger)(self.data[idx*2], self.data[idx*2+1]);
        }
    }

    /// Get single position value.
    fn get(&mut self, i: usize) -> T {
        self.data[self.bottom_offset+i]
    }

    /// Apply merge with v to single position [i, i+1).
    fn apply(&mut self, i: usize, v: T) {
        let mut idx = self.bottom_offset + i;
        while idx >= 1 {
            self.data[idx] = (self.merger)(self.data[idx], v);
            idx /= 2;
        }
    }

    /// Compute value [i, j).
    fn compute_range(&self, mut i: usize, mut j: usize) -> T {
        if i >= j {
            return self.default;
        }
        let mut result_left = self.default;
        let mut result_right = self.default;
        i += self.bottom_offset;
        j += self.bottom_offset;
        while i != j {
            if i & 1 == 1 {
                result_left = (self.merger)(result_left, self.data[i]);
                i += 1;
            }
            if j & 1 == 1 {
                j -= 1;
                result_right = (self.merger)(self.data[j], result_right);
            }
            i >>= 1;
            j >>= 1;
        }
        (self.merger)(result_left, result_right)
    }

    fn merge(&mut self, i: usize, j: usize) -> T {
        (self.merger)(self.data[i], self.data[j])
    }

    fn debug_print(&self, from: usize, to: usize) {
        for i in from..to {
            debug!(i, self.data[self.bottom_offset+i]);
        }
        debug!(from, to, self.compute_range(from, to));
    }
}

// ====


struct UnionFind {
      n: usize,
      parent: Vec<usize>,
      count: Vec<usize>
}

impl UnionFind {
     fn new(n: usize) -> Self {
           let mut p = vec![0; n];
           for i in 0..n {
                 p[i] = i;
           }
           UnionFind { n: n, parent: p, count: vec![1; n] }
     }

     fn find(&mut self, a: usize) -> usize {
           if self.parent[a] == a {
                 return a;
           }
           let par = self.parent[a];
           self.parent[a] = self.find(par);
           self.parent[a]
     }

     fn unite(&mut self, a: usize, b: usize) {
           let a = self.find(a);
           let b = self.find(b);
           if a == b {
                 return;
           }
           let ca = self.count[a];
           let cb = self.count[b];
           let total = ca + cb;
           self.count[b] = total;
           self.count[a] = total;
           if ca < cb {
                 self.parent[a] = b;
           } else {
                 self.parent[b] = a;
           }
     }

     fn same(&mut self, a: usize, b: usize) -> bool {
           self.find(a) == self.find(b)
     }

     fn count(&mut self, a: usize) -> usize {
           let a = self.find(a);
           self.count[a]
     }
}

// ====
const INF: i64 = 1e15 as i64;



fn main() {
    input! {
        n: usize, d: i64,
        a: [i64; n]
    };

    let mut left = SegmentTree::new(n, (INF, 0), Rc::new(|a,b| min(a,b)));
    let mut right = SegmentTree::new(n, (INF, 0), Rc::new(|a,b| min(a,b)));

    let mut pw = vec![];
    for i in 0..n {
        pw.push((a[i], i));
    }
    pw.sort();

    let mut edges = vec![];
    for i in 0..n {
        let a = pw[i].0;
        let idx = pw[i].1;
        let left_cost = left.compute_range(0, idx);
        let right_cost = right.compute_range(idx+1, n);

        if left_cost.0 < INF {
            let cost = a + left_cost.0 - ((n-idx) as i64)*d;
            edges.push((cost, idx, left_cost.1));
        }
        if right_cost.0 < INF {
            let cost = a + right_cost.0 - (idx as i64)*d;
            edges.push((cost, idx, right_cost.1));
        }

        left.set(idx, ((a+((n-idx) as i64)*d), idx));
        right.set(idx, ((a+(idx as i64)*d), idx));
    }

    edges.sort();

    let mut uf = UnionFind::new(n);
    let mut ans = 0;
    for (c, u, v) in edges {
        if uf.same(u, v) {
        } else {
            uf.unite(u, v);
            ans += c;
        }
    }
    println!("{}", ans);
}