#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;
int mx=0;
int main()
{
//vr1 + vr2 - floor(log2 (r2 - r1)).

int n;
cin>>n;
vector <int64_t> x(n),ind(n);
for(int i=0;i<n;i++)
    cin>>x[i],ind[i]=i;
int s=0;
do
{
    s=1;
    for(int i=0;i<n-1;i++)
        if(x[i]>x[i+1])
    {

        swap(x[i],x[i+1]);
        swap(ind[i],ind[i+1]);
        s=0;
    }
}while(!s);
for(int i=0;i<n;i++)
for(int j=i+1;j<n;j++)
    mx=std::max(mx,(int)(x[i]+x[j]-floor(log(abs(ind[j]-ind[i]))/log(2))));
cout<<mx;
}