#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")

#include <iostream>
#include <vector>
#include <cmath>

int64_t solve(const int n, const int k, const std::vector<int>& arr) {
    std::vector<int> rev(n);
    for (int i = 0; i < n; ++i) {
        rev[i] = arr[n-i-1];
    }
    int sum = 0;
    const int len = k / 2;
    std::vector<int> answ(n / 8);
    int64_t res = 0;
    for (int i = 0; i + k - 1 < n; ++i) {
        const int j = n - (i + k - 1) - 1;
        int begin = 0;
        const int size = len / 8;
        for (int id = 0; id < 8; ++id) {
            for (int t = 0; t < size; ++t) {
                answ[t] += std::abs(arr[i + id * size + t] - rev[j + id * size + t]);
            }
            begin += size;
        }
        for (int t = begin; t < len; ++t) {
            res += std::abs(arr[i+t] - rev[j+t]);
            //std::cout << "abs(" << i + t << " - " << j + t << ") = " << std::abs(arr[i+t] - rev[j+t]) << std::endl;
        }
        for (int i = 0; i < (int)answ.size(); ++i) {
            res += answ[i];
            answ[i] = 0;
        }
        //std::cout << res << std::endl;
    }
    return res;
}

int main() {
    int n, k;
    std::cin >> n >> k;
    std::vector<int> arr(n);
    for (auto &it : arr) { std::cin >> it; }
    std::cout << solve(n, k, arr) << std::endl;
    return 0;
}