#include <bits/stdc++.h>

using namespace std;
typedef pair <int, int> pii;

const int MAX_N = 400000 + 5;

int N, a[MAX_N];
pii b[MAX_N];
int c[MAX_N];

void add(int l, int r) {
    for (int i = l; i <= N + 1; i += i & -i) c[i] ++;
    for (int i = r + 1; i <= N + 1; i += i & -i) c[i] --;
}

int query(int x) {
    int res = 0;
    for (int i = x; i; i -= i & -i) res += c[i];
    return res;
}

bool check() {
    for (int i = 0; i < N; i ++)
        if (a[i] > a[i + 1]) return true;
    return false;
}

void simulate_odd() {
    for (int i = 0; i < N; i += 2)
        if (a[i] > a[i + 1]) swap(a[i], a[i + 1]);
}

int main() {
    scanf("%d", &N);
    for (int i = 0; i <= N; i ++) {
        scanf("%d", a + i);
    }
    if (!check()) {
        puts("0"); return 0;
    }
    simulate_odd();
    if (!check()) {
        puts("1"); return 0;
    }
    for (int i = 0; i <= N; i ++) {
        b[i] = make_pair(a[i], i);
    }
    sort(b, b + N + 1);
    int ans = 0;
    for (int i = 0; i <= N; i ++) {
        if (b[i].second < i) continue;
        int backward = b[i].second - i;
        int forward = query(b[i].second + 1);
        ans = max(forward * 2 + (forward & 1) + backward, ans);
        if (i < b[i].second) add(i + 1, b[i].second + 1);
    }
    printf("%d\n", ans + 1);
    return 0;
}