output_description: Format
  
  Print the minimum cost in one line. In the end put a line break.
input_description: Format
  
      
      
      N K
      a_1 a_2 a_3 ... a_N
attempt: #include <bits/stdc++.h>
  // #include <iostream>
  #include <vector>
  #include <algorithm>
  #include <string>
  #include <math.h>
  
  using namespace std;
  typedef long long ll;
  
  #define rep(i,n) for(int i=0;i<n;i++)
  #define rep2(i,a,b) for(int i=(a);i<(b);i++)
  
  template<class T> inline void chmin(T& a, T b) {if (a > b) a = b;}
  template<class T> inline void chmax(T& a, T b) {if (a < b) a = b;}
  const ll inf = 1LL<<60;
  
  int main() {
    int n,k,high;cin>>n>>k;
    ll ans=inf;
    ll now=0;
    int color=0;
  
    vector<int> a(n);
    rep(i,n){
      cin>>a[i];
    }
    for(int i=0;i<(1<<n);i++){
      high=a[0];
      color=1;
      now=0;
      for(int j=1;j<n;j++){
        if(1 & (i>>j)){
          if(a[j]<=high){
            now+=high-a[j]+1;
            high=high+1;
            color+=1;
          }else{
            color+=1;
          }
        }else{
          if(high<a[j]){
            high=a[j];
            color+=1;
          }
        }
      }
      if(k<=color){
        ans=min(ans,now);
      }
    }
    cout<<ans<<endl;
  }
  
problem_description: 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.
samples: [{"input": "5 5\n    3949 3774 3598 3469 3424", "output": "1541\n    \n\nThe optimal solution is (height of buildings from the left) = [3949, 3950,\n3951, 3952, 3953]."}, {"input": "5 3\n    7 4 2 6 4", "output": "7\n    \n\nThe optimal solution is (height of buildings from the left) = [7, 8, 2, 9, 4]."}]