#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N=1e6+10;
int n,a[2*N];
ll f[1010][1010];
int main()
{
    freopen("transportt.in","r",stdin);
    freopen("transportt.out","w",stdout);
    
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a[i];
        a[i+n]=a[i];
    }
    memset(f,0,sizeof(f));
    for(int len=2;len<=n;len++)
    {
        for(int l=1;l+len-1<=2*n;l++)
        {
            int r=l+len-1;
            int d=min(abs(l-r),n-abs(l-r));
            f[l][r]=a[l]+a[r]+d;
        }
    }
    ll mmax=0;
    for(int i=1;i<=n;i++) mmax=max(mmax,f[i][i+n-1]);
    cout<<mmax<<endl;
    return 0;
}