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

ans = 0
while any(abs(a[i - 1] - a[i]) > k for i in range(1, n)):
    for i in range(1, n):
        diff = abs(a[i - 1] - a[i])
        if diff > k:
            ans += diff - k
            if a[i - 1] < a[i]:
                a[i - 1] += diff - k
            else:
                a[i] += diff - k

print(ans)