//  ↘ ⬇ ⬇ ⬇ ⬇ ⬇ ↙
//  ➡ @roadfromroi ⬅
//  ↗ ⬆ ⬆ ⬆ ⬆ ⬆ ↖
#include <iostream>
#include "vector"
#include "algorithm"
#include "numeric"
#include "climits"
#include "iomanip"
#include "bitset"
#include "cmath"
#include "map"
#include "deque"
#include "array"
#include "set"
#include "boxes.h"
#define all(x) x.begin(), x.end()
using namespace std;
long long solve(int n, int k, int l, int * positions) {
    vector<long long> pos(n);
    for (int i = 0; i < n; ++i) {
        pos[i] = positions[i];
    }
    if (pos[0] == 0) {
        reverse(all(pos));
        pos.pop_back();
        reverse(all(pos));
        n--;
    }
    vector<long long> calcfrfr(n+1);
    for (int i = 0; i < n; ++i) {
        if (i < k) {
            calcfrfr[i+1] = pos[i] * 2;
        } else {
            calcfrfr[i+1] = pos[i] * 2 + calcfrfr[i+1-k];
        }
    }
    vector<long long> calcobr(n + 1);
    for (int i = n - 1; i >= 0; --i) {
        pos[i] = l - pos[i];
        if (i + k <= n) {
            calcobr[i] = pos[i] * 2 + calcobr[i + k];
        } else {
            calcobr[i] = pos[i] * 2;
        }
    }
    long long res = 1e18;
    for (int i = 0; i <= n; ++i) {
        res = min(res, calcfrfr[i] + calcobr[i]);
        if (i + k <= n) {
            res = min(res, calcfrfr[i] + calcobr[i+k] + l);
        }
    }
    if (n <= k)
        res = min(res, (long long)l);
    return res;
}
long long delivery(int N, int K, int L, int p[]) {
    return solve(N, K, L, p);
}