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 C (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <math.h>
#include <limits.h>
int max(int a, int b){return a>b?a:b;}
int min(int a, int b){return a<b?a:b;}
int gcd(int a, int b){return min(a,b)==0 ?max(a,b):gcd(min(a,b),max(a,b)%min(a,b));}
long long llmax(long long a, long long b){return a>b?a:b;}
long long llmin(long long a, long long b){return a<b?a:b;}
long long llgcd(long long a, long long b){return min(a,b)==0 ?max(a,b):gcd(min(a,b),max(a,b)%min(a,b));}
int assort(const void *a, const void *b){return *(int*)a-*(int*)b;}
int dessort(const void *a, const void *b){return *(int*)b-*(int*)a;}
int llassort(const void *a, const void *b){return *(long long*)a-*(long long*)b;}
int lldessort(const void *a, const void *b){return *(long long*)b-*(long long*)a;}
int charassort(const void *a, const void *b){return strcmp((char*)a ,(char*)b);}
int chardessort(const void *a, const void *b){return strcmp((char*)b ,(char*)a);}
char lowcmp[26]="abcdefghijklmnopqrstuvwxyz";
char upcmp[26]="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int ntoi(char c){return c-'0';}
int ltoi(char c){return c-'a';}
int utoi(char c){return c-'A';}
long long mod=1000000007;

int main(void){
    long long n,k;
    scanf("%lld%lld",&n,&k);
    long long a[n],ans=LLONG_MAX;
    for (int i=0; i<n; i++){
        scanf("%lld",&a[i]);
    }
    
    for (int i=0; i<(1<<n); i++){
        long long score=0,count=0,tmp=a[0];
        for (int j=0; j<n; j++){
            if ((1&i>>j)==1){
                count++;
            }
        }
        if (count>=k){
            for (int j=1; j<n; j++){
                if ((1&i>>j)==1){
                    if (a[j]<=tmp){
                        score+=tmp-a[j]+1;
                        tmp=tmp+1;
                    } else {
                        tmp=a[j];
                    }
                }
            }
            if (ans>score){
                ans=score;
            }
        }
    }
    printf("%lld\n",ans);
	return 0 ;
}