def workbook(n, k, arr):
    sp = 0
    page = 0
    
    for i in range(n):
        page += 1
        
        for j in range(1, arr[i]+1):
            if (j == page):
                sp += 1
            if (j % k == 0 and j!=arr[i]):
                page += 1
    
    return sp

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

result = workbook(n, k, arr)

print(result)