#include<bits/stdc++.h>
// #include<atcoder/all>
using namespace std;
// using namespace atcoder;
using lint = long long;
template<class T>using graph = vector<vector<T>>;
#define endl '\n'
int const INF = 1<<30;
lint const INF64 = 1LL<<62;
lint const mod = 1e9+7;
//long const mod = 998244353;


int main(){
    lint n,k;
    cin >> n >> k;
    lint a[n];
    for(int i=0;i<n;i++)cin >> a[i];
    lint summ = 0;
    lint plus = 0;
    for(int i=0;i<n;i++){
        summ += abs(a[i] - a[0]);
        if(i<k)plus += abs(a[i]-a[0]);
    }
    int left = 0;
    int right = k-1;
    lint ans = plus*2 - summ;
    for(lint i=1;i<n;i++){
        lint center = a[i];
        lint diff = a[i] - a[i-1];
        summ += (i - 1 - (n-1-i)) * diff;
        plus += (i - left - 1 - right + i) * diff;

        while(right < n-1){
            if(abs(a[left] - center) > abs(a[right+1] - center)){
                left++;
                right++;
                plus -= abs(a[left] - center);
                plus += abs(a[right+1] - center);
            }else{
                break;
            }
        }


        ans = min(ans, plus*2 - summ);
    }   
    cout << ans << endl;


}