// contest.cpp : アプリケーションのエントリ ポイントを定義します。
//

#include "bits/stdc++.h"
//実装が重そうな問題はある程度考えてから書く
//初期化を忘れずに（特に二分探索とか）
//コーナーケースを考えて（特に場合分けとか）
//不可解すぎるバグは配列外参照（配列の長さ）を検討
#define YES "YES"
#define NO "NO"
#define YESNO OUT(three(solve(),YES,NO))
#define ECHO OUT(solve())
#define three(A,B,C) ((A)?(B):(C))
#define FOR(i,a,b)  for(LL i=(a);i< (LL)(b);i++)
#define EFOR(i,a,b) for(LL i=(a);i<=(LL)(b);i++)
#define RFOR(i,a,b) for(LL i=(a);i>=(LL)(b);i--)
#define REP(i,b) FOR(i,zero,b)
#define EREP(i,b) EFOR(i,zero,b)
#define RREP(i,b) RFOR(i,b,zero)
#define ALL(c) c.begin(),c.end()
#define UNIQUE(c) sort(ALL(c));c.erase(unique(ALL(c)),c.end())
#define MAX(c) (*max_element(ALL(c)))
#define MIN(c) (*min_element(ALL(c)))
#define MP make_pair
#define FI first
#define SE second
#define SI(x) (LL(x.size()))
#define PB push_back
#define DEBUG(a) OUT(a)
#define DEBUG2(a,b) OUT2(a,b)
#define cat cout << __LINE__ << endl
#define OUT(a) cout << (a) << endl
#define OUT2(a,b) cout << (a) <<" "<<(b) << endl
#define int LL
#define zero 0LL
using namespace std;
template<typename T> inline void maximize(T &a, T b) { a = max(a, b); }
template<typename T> inline void minimize(T &a, T b) { a = min(a, b); }
template<typename T> inline bool middle(T a, T b, T c) { return b <= a && a <= c; }
template<class T> inline bool MX(T &l, const T &r) { return l < r ? l = r, 1 : 0; }
template<class T> inline bool MN(T &l, const T &r) { return l > r ? l = r, 1 : 0; }
typedef long long LL;
typedef double ld;
typedef LL ut;
typedef vector<int> VI;
typedef vector<VI> VII;
typedef pair < ut, ut > pr;
typedef pair<ut, pr> ppr;
typedef vector<pr> Vpr;
typedef vector<ppr> Vppr;
typedef priority_queue<pr, Vpr, greater<pr> > PQ;
inline void outputVI(VI x) { REP(i, SI(x)) { cout << three(i, " ", "") << x[i]; }OUT(""); }
const int SIZE1 = 5 * 1e5 + 1000;
const int SIZE2 = 5010;
const int SIZE3 = 400;
const int SIZE = SIZE1;
const LL p = 7 + 1e9;
const LL INF = 1LL << 60;
const long double EPS = 1e-7;
ut N, M, K, X, L, Y;
// ut A,B,C,D,E,F,G,H,I,J,O,P,Q,R,T,U;
LL vals[SIZE], nums[SIZE], maps[SIZE2][SIZE2], answer = zero;
VI edges[SIZE];
////////////////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////////////////
//LL L;
LL A[SIZE];
void init() {

}
LL solve2(int x) {
	LL ans = 0;
	LL lines = N - x;
	EFOR(i,1, x) {
		LL dist = A[i] - A[i - 1];
		LL num=(N - i + 1);
		LL plus = num % lines;
		LL formal = num / lines;
		ans += (formal + 1)*(formal + 1)*(lines - plus)*dist + (formal + 2)*(formal + 2)*(plus)*dist;
	}
	EFOR(i, x+1, N) {
		LL dist = A[i]-A[i-1];
		ans += (N - i+1)*dist*4;
		ans += A[i];
	}
	ans += X * N - X * x + X * N;
//	cout << x << " " << ans << endl;
	return ans;
}
LL solve() {
	cin >> N >> X;
	EFOR(i,1, N) {
		cin >> A[i];
	}
	int s = 0, e = N-1;
	REP(i, N) {
//		cout << i << " "<<solve2(i) << endl;
	}
	while (s < e) {
	//	cout << s << " " << e << endl;
	//	cout << solve2(s) << " " << solve2(e) << endl;
		int f2 = s+((e-s)*2+1.5) / 3;
		int f1 = s+(e-s) / 3;
		if (solve2(f1)>=solve2(f2)) {
			s = f1+1;
		}
		else {
			e = f2-1;
		}
		
	}
	//cout << s << " " << e << endl;
	cout << solve2(s) << endl;
	return 0;
}
signed main() {
	solve();
	return 0;
}

Measured memory_bytes: 16128