#include <iostream>
#include <vector>
using namespace std;

int i,j,K,N,koltseg,magassag,mini=INT_MAX;
vector <int>v;

int main()
{
    cin>>N;
    cout<<" ";
    cin>>K;
    v.resize(N+1);
    for (i=1;i<=N;++i)
        cin>>v[i];

    for (i=1;i<=N-K+1;++i)
    {
        koltseg=0;
        magassag=v[i+K-1];
        for(j=i+K-1;j>i;--j)
            if(v[j-1]<=magassag)
        {
            koltseg+=magassag-v[j-1]+1;
            magassag++;
        }
        else
        {
            koltseg+=(v[j-1]-magassag-1)*(i+K-j);
            magassag=v[j-1];
        }
        if(koltseg<mini) mini=koltseg;
    }
    cout<<mini;
}