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n, k = map(int, input().split())
heights = list(map(int, input().split()))

result = 0
for i in range(1,n,1):
    for j in range(i-1,-1,-1):
        if heights[j+1] > heights[j] + k:
            result += heights[j+1] - k - heights[j]
            heights[j] = heights[j+1] - k
        elif heights[j] > heights[j+1] + k:
            result += heights[j] - k - heights[j+1]
            heights[j+1] = heights[j] - k
print(result)