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# import sys
# sys.stdin = open("tra.txt", "r")

import heapq

n, k = map(int, input().split())
sciez = list(map(int, input().split()))
heap = [(-wys, index) for index, wys in enumerate(sciez)]
obsluzone = set()
heapq.heapify(heap)
ciezarowek = 0
while (len(obsluzone) < n):
    wys, index = heapq.heappop(heap)
    wys = -wys
    if not index in obsluzone:
        obsluzone.add(index)
        if (index > 0) and (not (index-1) in obsluzone):
            roz = sciez[index] - sciez[index-1]
            if roz > k:
                ciezarowek+= roz-k
                sciez[index-1]+= roz-k
                heapq.heappush(heap, (-sciez[index-1], index-1))
        if (index < n-1) and (not (index+1) in obsluzone) :
            roz = sciez[index] - sciez[index+1]
            if roz > k:
                ciezarowek+= roz-k
                sciez[index+1]+= roz-k
                heapq.heappush(heap, (-sciez[index+1], index+1))
        
print(ciezarowek)