#include <iostream>
#include <cmath>

#define NMAX 100007
#define INF (1 << 30)

using namespace std;

int n;
int a[NMAX], Max, Max2, poz, poz2, Ans;

int main(){
    cin >> n;
    Max = -INF;
    Max2 = -INF;
    Ans = -INF;
    for(int i = 1; i <= n; ++i){
        cin >> a[i];
        Max = max(Max, a[i]);
        if(Max == a[i])
            poz = i;
    }
    for(int i = 1; i <= n; ++i)
        if(poz != i)
            Ans = max(Ans, a[poz] + a[i] - (int)log(fabs(poz - i)));
    for(int i = 1; i <= n; ++i)
        if(Max != a[i]){
            Max2 = max(Max2, a[i]);
            if(Max2 == a[i])
                poz2 = a[i];
        }
    for(int i = 1; i <= n; ++i)
        if(poz2 != i)
            Ans = max(Ans, a[poz2] + a[i] - (int)log(fabs(poz2 - i)));
    cout << Ans;
    return 0;
}