#include <bits/stdc++.h>
using namespace std;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

int main() {
    int64_t n, k; cin >> n >> k;
    auto a = vec<int64_t>(uns, n);
    for (auto &e : a) cin >> e;

    auto pos = [&]() {
        int64_t prev = 0;
        for (int i = 0; i < k; ++i) {
            prev += abs(a[i] - a[k / 2]);
        }

        int pos = k / 2;
        int64_t sub = prev;
        for (int i = k / 2 + 1; i < n - (k - 1) / 2; ++i) {
            auto cnt = prev;
            cnt -= abs(a[i - k / 2 - 1] - a[i - 1]);
            cnt += abs(a[i + (k - 1) / 2] - a[i]);
            cnt += abs(a[i] - a[i - 1]) * (k / 2);
            cnt -= abs(a[i] - a[i - 1]) * ((k - 1) / 2);

            if (cnt < sub) {
                pos = i;
                sub = cnt;
            }

            prev = cnt;
        }

        return pos;
    }();

    auto ans = [&]() {
        int64_t prev = 0;
        for (int i = 0; i < n; ++i) {
            if (pos - k / 2 <= i && i < pos + (k + 1) / 2) {
                prev += abs(a[i] - a[pos - k / 2]);
            }
            else {
                prev -= abs(a[i] - a[pos - k / 2]);
            }
        }

        int64_t ans = prev;
        for (int i = pos - k / 2 + 1; i < pos + (k + 1) / 2; ++i) {
            auto cnt = prev;
            auto d = a[i] - a[i - 1];
            cnt -= d * (pos - k / 2);
            cnt += d * (i - (pos - k / 2));
            cnt -= d * (pos + (k + 1) / 2 - i);
            cnt += d * (n - (pos + (k + 1) / 2));

            ans = min(ans, cnt);
            prev = cnt;
        }

        return ans;
    }();

    cout << ans << endl;
}