//Dragan Andrei Gabriel
//University of Bucharest

#include <cstdio>
#include <cassert>
#include <cmath>
#include <cstring>
#include <ctime>
#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <istream>
#include <ostream>
#include <deque>
#include <map>
#include <queue>
#include <stack>
#include <climits>
#include <set>
#include <vector>
#include <algorithm>
#include <functional>
#include <string>
#include <utility>
using namespace std;

long long v[100001], rez;
int n, i, j, k, x, y;

int main()
{
    #ifndef ONLINE_JUDGE
    freopen("a.in", "r", stdin);
    freopen("a.out", "w", stdout);
    #endif

    rez = LONG_MIN;
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
        scanf("%lld", &v[i]);

    for (int i = 1; i < n; i++)
        for (int j = i + 1; j <= n; j++)
        {
            rez = max (rez, 1LL *(v[i] + v[j] - (long long)floor(log2(j - i))));
        }

    printf("%lld\n", rez);
    return 0;
}