A sequence a0, a1, ..., at - 1 is called increasing if ai - 1 < ai for each i: 0 < i < t.

You are given a sequence b0, b1, ..., bn - 1 and a positive integer d. In each move you may choose one element of the given sequence and add d to it. What is the least number of moves required to make the given sequence increasing?

Input

The first line of the input contains two integer numbers n and d (2 ≤ n ≤ 2000, 1 ≤ d ≤ 106). The second line contains space separated sequence b0, b1, ..., bn - 1 (1 ≤ bi ≤ 106).

Output

Output the minimal number of moves needed to make the sequence increasing.

Examples

Input

4 2
1 3 3 2


Output

3
def rr(): return input().rstrip()
def rri(): return int(rr())
def rrl(): return list(map(int, rr().split()))
def rrt(): return tuple(map(int, rr().split()))
from collections import defaultdict
def mus(d=lambda: 0): return defaultdict(lambda: defaultdict(d))
def dd0(d=lambda: 0): return defaultdict(d)
def ms(x, y, d=0): return [[0]*y for i in range(x)]
def ar(x, d=0): return [d]*x
def ppm(m, n=0, x=0, y=0): print("\n".join(("\t".join((str(m[j][i]) for j in range(y or n))) for i in range(x or n))))
def ppa(a, n): print("\t".join(map(str, a[0:n])))
def ppl(a=0, x=[1]): x[0]=a or (x[0]+1); print("-"+"- -"*14+"-# "+str(x[0]-2)+" #-"+"- -"*14+"-")
def fltn(a): (i for sub in a for i in sub)
def yn(x): return "YES" if x else "NO"
from itertools import accumulate
from itertools import groupby
def grp(x): return ((i, sum(1 for _ in g)) for i, g in groupby(x))
import math
def rnar(): return (*rrl(), rrl())
def rn(): return (*rrl(),)
def dpp(a, b=""): print(")#| {} |#(o) ? {} ? (".format(a, b))

def read():
    return rnar()
    return (0,)

def solve(n, d, arr):
    
    am_of_mvs = 0
    for i in range(len(arr)-1):
        if arr[i] >= arr[i+1]:
            am = (arr[i] - arr[i+1])//d + 1
            #print(am)
            am_of_mvs += am
            arr[i+1] += d*am
    ans = am_of_mvs
    return ans

if __name__ == "__main__":
    #test_count = rri()
    test_count = 1
    for _ in range(test_count):
        input_data = read()
        result = solve(*input_data)
        print(result)
