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

int n;
cin>>n;
vector <int64_t> x(n);
for(int i=0;i<n;i++)
    cin>>x[i];
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(j-i)/log(2))));
cout<<mx;
}