C++ :

#include<iostream>
#include<algorithm>
#include<cstring>
#include<ctime>
#include<cmath>
#include<string>
#include<vector>
#include<cstdio>
using namespace std;

const int N = 10010;
int d[N], c1[N], c2[N];

void longest_inc_seq(int* a, int n, bool f) {
    int *t = new int[n], len = 0;
    t[len] = a[0];
    f ? c1[0] = 1 : c2[0] = 1;
    for(int i = 1; i < n; ++i) {
        if(a[i] > t[len]) {
            t[++len] = a[i];
            f ? c1[i] = len + 1 : c2[i] = len + 1;
        }
        else {
            int p = lower_bound(t, t + len + 1, a[i]) - t;
            t[p] = a[i];
            f ? c1[i] = p + 1 : c2[i] = p + 1;
        }
    }
    free(t);
}

int main() {
    int n, i, j;
    while(~scanf("%d", &n)) {
        for(i = 0; i < n; ++i) scanf("%d", &d[i]), c1[i] = c2[i] = 0;
        longest_inc_seq(d, n, true);
        i = 0, j = n - 1;
        while(i < j) swap(d[i++], d[j--]);
        longest_inc_seq(d, n, false);
        int ans = 0;
        for(i = 0; i < n; ++i)
            ans = max( 2 * min(c1[i], c2[n-i-1]) - 1, ans );
        printf("%d\n", ans);
    }
    return 0;
}