#include <iostream>
#include <fstream>
using namespace std;
#define MAX 100010
#define INF (1<<30) + 2
int n, doi[MAX], a[2 * MAX][21];

int intre(int i, int j)
{
    int lg = j - i + 1;
    lg = doi[lg];
    return max(a[i][lg], a[j - (1 << lg) + 1][lg]);
}

int main()
{
    int i, j;
    long long best = 2ll * (-INF);
    cin >> n;
    doi[1] = 0;
    for(i = 1 ; i <= n ; i++)
    {
        if(i - 1)
            doi[i] = doi[i / 2] + 1;
        cin >> a[i][0];
        a[i + n][0] = -INF;
    }
    for(j = 1 ; (1 << j) <= 2 * n ; j++)
    {
        for(i = 1 ; i <= n ; i++)
        {
            a[i][j] = max(a[i][j - 1], a[i + (1<<(j - 1))][j - 1]);
           // cout << a[i][j] << " ";
        }
       // cout << "\n";
    }
    for(i = 1 ; i < n ; i ++)
    {
        for(j = 0 ; i + (1 << j) <= 2 * n ; j++)
        {
            //cout << i << " " << j << " " << a[i][0] << " " << a[i + 1][j] << " " << j << "\n";
            best = max(best, 1ll * a[i][0] + intre(i + 1, min(n, i + (1 << (j + 1)) - 1)) - j);
            //cout << i + 1 << ' ' << min(n, i + (1 << (j + 1)) - 1) << "\n";
           // cout << i << " " << j << " " << best << "\n";
        }
    }
    cout << best << "\n";

}