1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
def zadanie(a, n, k):
    b = a[:] 
    
    for i in range(1, n):
        if b[i] < b[i-1] - k:
            b[i] = b[i-1] - k
    
    for i in range(n-2, -1, -1):
        if b[i] < b[i+1] - k:
            b[i] = b[i+1] - k
    
    return sum(b[i] - a[i] for i in range(n))

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

print(zadanie(a, n, k))