#include "bits/stdc++.h"

using namespace std;

#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl

typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define rep1(i,n) for(ll i=1;i<=(ll)(n);i++)
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define rrep1(i,n) for(ll i=(ll)(n);i>0;i--)
#define REP(i,a,b) for(ll i=(ll)a;i<(ll)b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = 2e18;
const ll MOD = 1000000007;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { 1,0, -1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);


class LazySegmentTree {
public:
	int n;
	vl node, lazy;
	bool ismax; //trueなら最大値、falseなら最小値

	LazySegmentTree(vl a, bool _ismax) {
		ismax = _ismax;
		int _n = a.size();
		n = 1; while (n < _n) n *= 2;
		node.resize(2 * n - 1);
        fill(all(node), INF * (1 - (int)ismax * 2));
		lazy.resize(2 * n - 1, 0);
		for (int i = 0; i < _n; i++) node[i + n - 1] = a[i];
		for (int i = n - 2; i >= 0; i--) {
			if (ismax) node[i] = max(node[i * 2 + 1], node[i * 2 + 2]);
			else node[i] = min(node[i * 2 + 1], node[i * 2 + 2]);
		}
	}

	// k番目のノードについて遅延評価を行う
	inline void eval(int k, int l, int r) {
		if (lazy[k] != 0) {
			node[k] += lazy[k];
			if (r - l > 1) {
				lazy[2 * k + 1] += lazy[k]; /////
				lazy[2 * k + 2] += lazy[k]; /////
			}
			lazy[k] = 0;
		}
	}

	void add(int a, int b, ll x, int k, int l, int r) {
		// k 番目のノードに対して遅延評価を行う
		eval(k, l, r);
		if (b <= l || r <= a) return;
		if (a <= l && r <= b) {
			lazy[k] += x; //////
			eval(k, l, r);
		}
		else {
			add(a, b, x, 2 * k + 1, l, (l + r) / 2);
			add(a, b, x, 2 * k + 2, (l + r) / 2, r);
			if (ismax) node[k] = max(node[2 * k + 1], node[2 * k + 2]);
			else node[k] = min(node[2 * k + 1], node[2 * k + 2]);
		}
	}

	ll getmax(int a, int b, int k, int l, int r) {
		eval(k, l, r);
		if (b <= l || r <= a) return (ismax ? -INF : INF);
		if (a <= l && r <= b) return node[k];
		ll resl = getmax(a, b, 2 * k + 1, l, (l + r) / 2);
		ll resr = getmax(a, b, 2 * k + 2, (l + r) / 2, r);
		if (ismax) return max(resl, resr);
		else return min(resl, resr);
	}

};



int main () {
  int n, q, a, b;
  cin >> n >> q >> a >> b;
  a--; b--;
  vi x(q + 1);
  x[0] = a;
  rep1 (i, q) {
    cin >> x[i];
    x[i]--;
  }
  vl c(n, INF / 100);
  c[b] = 0;
  LazySegmentTree lst(c, false);
  vl c2 = c;
  rep (i, n) {
    c2[i] += (n - 1 - i);
  }
  LazySegmentTree lst2(c2, false);
  c2 = c;
  rep (i, n) {
    c2[i] += i;
  }
  LazySegmentTree lst3(c2, false);
  rep1 (i, q) {
    ll mi1 = lst2.getmax(0, x[i] + 1, 0, 0, lst2.n), mi2 = lst3.getmax(x[i], lst3.n, 0, 0, lst3.n);
    ll mi = min(mi1 - (n - 1 - x[i]), mi2 - x[i]);
    lst.add(0, n, abs(x[i] - x[i - 1]), 0, 0, lst.n);
    lst2.add(0, n, abs(x[i] - x[i - 1]), 0, 0, lst2.n);
    lst3.add(0, n, abs(x[i] - x[i - 1]), 0, 0, lst3.n);
    ll temp = lst.getmax(x[i - 1], x[i - 1] + 1, 0, 0, lst.n);
    if (temp > mi) {
      lst.add(x[i - 1], x[i - 1] + 1, -temp, 0, 0, lst.n);
      lst.add(x[i - 1], x[i - 1] + 1, mi, 0, 0, lst.n);
      lst2.add(x[i - 1], x[i - 1] + 1, -temp, 0, 0, lst2.n);
      lst2.add(x[i - 1], x[i - 1] + 1, mi, 0, 0, lst2.n);
      lst3.add(x[i - 1], x[i - 1] + 1, -temp, 0, 0, lst3.n);
      lst3.add(x[i - 1], x[i - 1] + 1, mi, 0, 0, lst3.n);
    }
    /*
    cout << "lst" << endl;
    rep (j, n) {
      cout << lst.getmax(j, j + 1, 0, 0, lst.n) << " ";
    }
    cout << endl;
    cout << "lst2" << endl;
    rep (j, n) {
      cout << lst2.getmax(j, j + 1, 0, 0, lst2.n) << " ";
    }
    cout << endl;
    cout << "lst" << endl;
    rep (j, n) {
      cout << lst3.getmax(j, j + 1, 0, 0, lst3.n) << " ";
    }
    cout << endl;
    DEBUG(lst.getmax(0, n, 0, 0, lst.n));
    //*/
  }
  cout << lst.getmax(0, n, 0, 0, lst.n) << endl;
}

    


Measured memory_bytes: 32356