// Copyright (C) 2017 __debug.

// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; version 3

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program; If not, see <http://www.gnu.org/licenses/>.


#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/priority_queue.hpp>

#define x first
#define y second
#define MP std::make_pair
#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(), (x).end()
#define DEBUG(...) fprintf(stderr, __VA_ARGS__)
#ifdef __linux__
#define getchar getchar_unlocked
#define putchar putchar_unlocked
#endif

using std::pair;
using std::vector;
using std::string;

typedef long long LL;
typedef pair<int, int> Pii;

const int oo = 0x3f3f3f3f;

template<typename T> inline bool chkmax(T &a, T b) { return a < b ? a = b, true : false; }
template<typename T> inline bool chkmin(T &a, T b) { return b < a ? a = b, true : false; }
string procStatus()
{
    std::ifstream t("/proc/self/status");
    return string(std::istreambuf_iterator<char>(t), std::istreambuf_iterator<char>());
}
template<typename T> T read(T &x)
{
    int f = 1;
    char ch = getchar();
    for (; !isdigit(ch); ch = getchar())
        f = (ch == '-' ? -1 : 1);
    for (x = 0; isdigit(ch); ch = getchar())
        x = 10 * x + ch - '0';
    return x *= f;
}
template<typename T> void write(T x)
{
    if (x == 0) {
        putchar('0');
        return;
    }
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    static char s[20];
    int top = 0;
    for (; x; x /= 10)
        s[++top] = x % 10 + '0';
    while (top)
        putchar(s[top--]);
}
// EOT

const int MAXN = 2e5 + 5;

int N, M;
LL A[MAXN];

void input()
{
    read(M); read(N);
    for (int i = 0; i <= N + 1; ++i) {
        read(A[i]);
    }
}

struct SEGT {
    static const int SIZE = (1 << 19) + 5;

    LL min[SIZE];

#define LC (u << 1)
#define RC (u << 1 | 1)

    SEGT() { memset(min, +oo, sizeof(min)); }

    void update(int u, int l, int r, int ql, int qr, LL x)
    {
        if (ql <= l && r <= qr) {
            chkmin(min[u], x);
            return;
        }
        int mid = (l + r) >> 1;
        if (ql <= mid) update(LC, l, mid, ql, qr, x);
        if (mid < qr) update(RC, mid + 1, r, ql, qr, x);
    }

    LL query(int u, int l, int r, int p)
    {
        if (l == r) return min[u];
        int mid = (l + r) >> 1;
        return std::min(min[u], p <= mid ? query(LC, l, mid, p) : query(RC, mid + 1, r, p));
    }

};

void solve()
{
    static LL S[MAXN];

    for (int i = 0; i <= N; ++i) {
        S[i+1] = S[i] + std::abs(A[i] - A[i+1]);
    }

    static LL dp[MAXN];
    static SEGT s0, s1;

    for (int i = N; i >= 1; --i) {
        dp[i] = std::min(S[N+1] - S[i], S[N] - S[i] + std::abs(A[N+1] - A[i-1]));
        chkmin(dp[i], s0.query(1, 1, M, A[i-1]) - S[i] - A[i-1]);
        chkmin(dp[i], s1.query(1, 1, M, A[i-1]) - S[i] + A[i-1]);
        s0.update(1, 1, M, 1, A[i], dp[i] + S[i-1] + A[i]);
        s1.update(1, 1, M, A[i], M, dp[i] + S[i-1] - A[i]);
    }

    printf("%lld\n", dp[1]);
}

int main()
{
#ifdef __DEBUG
    freopen("F.in", "r", stdin);
    freopen("F.out", "w", stdout);
#endif

    input();
    solve();

    return 0;
}

// 无言独上西楼，月如钩。寂寞梧桐深院锁清秋。
//     -- 李煜《相见欢·无言独上西楼》


Measured memory_bytes: 13184