#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define subnb true
#define Lnb true
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

const int N = (int)4e5 + 50;
const int INF = (int)1e9;
#define lson(x) 2*x+1
#define rson(x) 2*x+2

struct node {
    ll mx, add;
    void add_val(int x) {
        add += x;
        mx += x;
    }

    void merge(node &ls, node &rs) {
        mx = max(ls.mx, rs.mx);
    }
};

struct Tree {
    node dat[N * 4];

    void init(int n) {
        fill(dat, dat + 4 * n, node{-INF, 0});
    }
    void push_down(int x, int l, int r) {
        if(dat[x].add) {
            if(l < r) {
                dat[lson(x)].add_val(dat[x].add);
                dat[rson(x)].add_val(dat[x].add);
            }
            dat[x].add = 0;
        }
    }
    void update(int a, int b, int x, int l, int r, int d) {
        int mid = (l + r) / 2;
        if(r < a || l > b) return;
        push_down(x, l, r);
        if(l >= a && r <= b) {
            dat[x].add_val(d);
            return;
        }
        update(a, b, lson(x), l, mid, d);
        update(a, b, rson(x), mid + 1, r, d);
        dat[x].merge(dat[lson(x)], dat[rson(x)]);
    }

    void upd(int pos, int x, int l, int r, int val) {
        if(l == r) {
            dat[x] = {val, 0};
            return;
        }
        push_down(x, l, r);
        int mid = (l + r) / 2;
        if(pos <= mid) upd(pos, lson(x), l, mid, val);
        else upd(pos, rson(x), mid + 1, r, val);
        dat[x].merge(dat[lson(x)], dat[rson(x)]);

    }
//    int query(int a, int b, int x, int l, int r) {
//        int mid = (l + r) / 2;
//        if(r < a || l > b) return -INF;
//        push_down(x, l, r);
//        if(l >= a && r <= b) return dat[x].mx;
//        return max(query(a, b, lson(x), l, mid), query(a, b, rson(x), mid + 1, r));
//    }

} tree;

int n;
int a[N];
vector<pii> ps;
int in[N];
int pf = 0;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    cin >> n;
    n++;
    rep(i, 0, n) cin >> a[i], ps.push_back({a[i], i});
    sort(all(ps));
    tree.init(n);
    ll res = 0;
    int c = 0;
    for (auto p : ps) {
        c++;
        tree.update(0, p.second - 1, 0, 0, n - 1, 2);
        tree.update(p.second, p.second, 0, 0, n - 1, p.second + (p.second % 2 == 0) + INF);

        in[p.second] = 1;
        while(pf < n && in[pf]) {
            if(pf % 2 == 0) tree.upd(pf, 0, 0, n - 1, -INF);
            pf++;
        }
        if(pf == c) {
            continue;
        }
//        cout << pf << endl;
//
//        cout << p.first << " " << tree.dat[0].mx - (c - 1) << endl;

        res = max(res, tree.dat[0].mx - (c - 1));
    }
    cout << res << endl;



}