#include<bits/stdc++.h>
using namespace std;
#define ml n/2
int n,d[1000001],ans=-1;
class C{
	public:
		int bh,qz;
		bool operator < (const C &y) const{
			if(qz!=y.qz)return qz>y.qz;
			else return bh<y.bh; 
		}
}e[1000001];
int main(){
	freopen("transportt.in","r",stdin);
	freopen("transportt.out","w",stdout);
	cin>>n;
	for(int i=1;i<=n;i++){
		scanf("%d",&d[i]);
		e[i]=C{i,d[i]};
	}
	stable_sort(e+1,e+n+1);
	for(int i=1;i<5000;i++){
		for(int j=i+1;j<=5000;j++){
			ans=max(ans,e[i].qz+e[j].qz+min(n-abs(e[i].bh-e[j].bh),abs(e[i].bh-e[j].bh)));
		}
	}
	cout<<ans;
	fclose(stdin);
	fclose(stdout);
	return 0;
}