Problem:
Max Score: 350 Points

Problem Statement

There are N buildings along the line. The i-th building from the left is colored in color i, and its height is currently a_i meters.

Chokudai is a mayor of the city, and he loves colorful thigs. And now he wants to see at least K buildings from the left.

You can increase height of buildings, but it costs 1 yens to increase 1 meters. It means you cannot make building that height is not integer.

You cannot decrease height of buildings.

Calculate the minimum cost of satisfying Chokudai's objective.

Note: "Building i can see from the left" means there are no j exists that (height of building j) ≥ (height of building i) and j < i.

Input Format

N K
a_1 a_2 a_3 ... a_N

Output Format

Print the minimum cost in one line. In the end put a line break.

Constraints

1 ≤ K ≤ N ≤ 15

1 ≤ a_i ≤ 10^9

Scoring

Subtask 1 [120 points]

N = K

Subtask 2 [90 points]

N ≤ 5

a_i ≤ 7

Subtask 3 [140 points]

There are no additional constraints.

Sample Input 1

5 5
3949 3774 3598 3469 3424

Sample Output 1

1541

The optimal solution is (height of buildings from the left) = [3949, 3950, 3951, 3952, 3953].

Sample Input 2

5 3
7 4 2 6 4

Sample Output 2

7

The optimal solution is (height of buildings from the left) = [7, 8, 2, 9, 4].

Solution in Python (3.4.3) (judge verdict: Runtime Error)

import copy
n, k = map(int, input().split())
alist = list(map(int, input().split()))

ans = 10**20
count = 0
tempbin = ""
maxx = 0

for i in range(2**n):
    tempbin = format(i,'b')
    tempbin = tempbin.zfill(n)
    count = 0
    templist = alist.copy()
    if tempbin.count("1") != k:
        continue
    for j in range(1,n):
        if tempbin[j] == "1":
            maxx = max(templist[:j])
            if maxx >= templist[j]:
                count += maxx + 1 - templist[j]
                templist = maxx + 1
    ans = min(ans,count)

print(ans)