using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.IO;
using System.Reflection;
using static System.Math;
using System.Numerics;
//using nint=System.Int32;
static class Program{
	const int mod=(int)1e9+7;
	const double eps=1e-11;
	static void Main(){
		Sc sc=new Sc();
		var n=sc.I;
		var a=sc.Ia;
		var wm=new Wm(a);
		Spt spt=new Spt(a,false);
		int ans=int.MaxValue;
		for(int i = 1;i<n-1;i++) {
			int c=wm.Nv(0,i-1,a[i]);
			int d=wm.Nv(i+1,n-1,a[i]);
			if(c!=-1&&d!=-1){ans=Min(ans,c+a[i]+d);}
			c=spt.Get(0,i-1);
			d=spt.Get(i+1,n-1);
			if(c<a[i]&&d<a[i]){ans=Min(ans,c+a[i]+d);}
		}
		Console.WriteLine("{0}",ans==int.MaxValue?-1:ans);
	}
}
public class Spt{
	private readonly int[][] d;
	private readonly int[] l;
	private Func<int,int,int> Fu;
	public Spt(int[] a,bool bo){
		int n=a.Length,m=(int)Log(n,2)+1;
		d=new int[m][];
		d[0]=new int[n];
		l=new int[n+1];
		if(bo){Fu=(y,x)=>Max(y,x);}
		else{Fu=(y,x)=>Min(y,x);}
		for(int i=0;i<n;i++){
			d[0][i]=a[i];
			l[i+1]=l[i>>1]+1;
		}
		for(int i=1,k=1;i<m;i++,k<<=1){
			int p=n+1-(k<<1);
			d[i]=new int[p];
			for(int j=0;j<p;j++){d[i][j]=Fu(d[i-1][j],d[i-1][j+k]);}
		}
	}
	public int Get(int a,int b){
		if(a>b){(a,b)=(b,a);}
		int p=l[b-a];
		return Fu(d[p][a],d[p][b+1-(1<<p)]);
	}
}
public class Wm{
	private int[][] ra;
	private int[] za;
	private const int b=30;
	private int n;
	public Wm(int[] a){
		n=a.Length;
		var d=new int[b+1][];
		ra=new int[b+1][];
		for(int i = 0;i<=b;i++) {
			d[i]=new int[n];
			ra[i]=new int[n+1];
		}
		var d0=new int[2][]{new int[n],new int[n]};
		var d1=new int[2][]{new int[n],new int[n]};
		var h0=new int[]{0,0};
		var h1=new int[]{0,0};
		za=new int[b+1];
		for(int i = 0;i<n;i++) {
			if((a[i]&(1<<b))==0){
				d0[1][h0[1]]=a[i];
				h0[1]++;
				za[b]++;
			}
			else{
				d1[1][h1[1]]=a[i];
				h1[1]++;
				d[b][i]=ra[b][i+1]=1;
			}
			ra[b][i+1]+=ra[b][i];
		}
		for(int i = 1;i<=b;i++) {
			int g=(1<<(b-i)),p=i&1;
			h0[p^1]=h1[p^1]=0;
			for(int j = 0;j<h0[p];j++) {
				if((d0[p][j]&g)==0){
					d0[p^1][h0[p^1]]=d0[p][j];
					h0[p^1]++;
					za[b-i]++;
				}
				else{
					d1[p^1][h1[p^1]]=d0[p][j];
					h1[p^1]++;
					d[b-i][j]=ra[b-i][j+1]=1;
				}
				ra[b-i][j+1]+=ra[b-i][j];
			}
			for(int j = 0;j<h1[p];j++) {
				if((d1[p][j]&g)==0){
					d0[p^1][h0[p^1]]=d1[p][j];
					h0[p^1]++;
					za[b-i]++;
				}
				else{
					d1[p^1][h1[p^1]]=d1[p][j];
					h1[p^1]++;
					d[b-i][h0[p]+j]=ra[b-i][h0[p]+j+1]=1;
				}
				ra[b-i][h0[p]+j+1]+=ra[b-i][h0[p]+j];
			}
		}
	}
	public int Rk(int l,int r,long k){
		l--;
		for(int i = b;i>=0;i--) {
			if(((k>>i)&1)==1){
				r=ra[i][r+1]+za[i]-1;
				l=ra[i][l+1]+za[i]-1;
			}
			else{
				r=r-ra[i][r+1];
				l=l-ra[i][l+1];
			}
		}
		return r-l;
	}
	public int Rl(int l,int r,long k){
		l--;
		int p=0;
		for(int i = b;i>=0;i--) {
			if(((k>>i)&1)==1){
				p+=r-l;
				r=ra[i][r+1]+za[i]-1;
				l=ra[i][l+1]+za[i]-1;
				p-=r-l;
			}
			else{
				r=r-ra[i][r+1];
				l=l-ra[i][l+1];
			}
		}
		return p;
	}
	public int Rm(int l,int r,long k){
		l--;
		int p=0;
		for(int i = b;i>=0;i--) {
			if(((k>>i)&1)==1){
				r=ra[i][r+1]+za[i]-1;
				l=ra[i][l+1]+za[i]-1;
			}
			else{
				p+=r-l;
				r=r-ra[i][r+1];
				l=l-ra[i][l+1];
				p-=r-l;
			}
		}
		return p;
	}
	public int Qt(int l,int r,int k){
		l--;
		int p=0;
		for(int i = b;i>=0;i--) {
			if((r-ra[i][r+1])-(l-ra[i][l+1])<k){
				k-=(r-ra[i][r+1])-(l-ra[i][l+1]);
				r=ra[i][r+1]+za[i]-1;
				l=ra[i][l+1]+za[i]-1;
				p|=1<<i;
			}
			else{
				r=r-ra[i][r+1];
				l=l-ra[i][l+1];
			}
		}
		return p;
	}
	public int Pv(int l,int r,int k){
		int p=Rl(l,r,k);
		return p!=0?Qt(l,r,p):-1;
	}
	public int Nv(int l,int r,int k){
		int p=Rm(l,r,k);
		return p!=0?Qt(l,r,r-l+1-p+1):-1;
	}
}
public class Sc{
	public int I{get{return int.Parse(Console.ReadLine());}}
	public long L{get{return long.Parse(Console.ReadLine());}}
	public double D{get{return double.Parse(Console.ReadLine());}}
	public string S{get{return Console.ReadLine();}}
	public int[] Ia{get{return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
	public object[] Oa{get{return Console.ReadLine().Split();}}
	public int[] Ia2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),int.Parse);}}
	public int[] Ia3(string a,string b){return Array.ConvertAll((a+Console.ReadLine()+b).Split(),int.Parse);}
	public int[] Ia3(int a){return Array.ConvertAll((Console.ReadLine()+" "+a.ToString()).Split(),int.Parse);}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),long.Parse);}}
	public long[] La3(string a,string b){return Array.ConvertAll((a+Console.ReadLine()+b).Split(),long.Parse);}
	public long[] La3(int a){return Array.ConvertAll((Console.ReadLine()+" "+a.ToString()).Split(),long.Parse);}
	public double[] Da2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),double.Parse);}}
	public double[] Da3(string a,string b){return Array.ConvertAll((a+Console.ReadLine()+b).Split(),double.Parse);}
	public T[] Arr<T>(int n,Func<T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f();}return a;}
	public T[] Arr<T>(int n,Func<int,T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i);}return a;}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Console.ReadLine().Split());}return a;}
	public T[] Arr<T>(int n,Func<int,string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i,Console.ReadLine().Split());}return a;}
}