#include <iostream>

 #include <cstring>

 #include <cstdio>

 #include <algorithm>

 using namespace std;

 int a[];

 int main()

 {

     int n;

     bool f;

     while(~scanf("%d",&n))

     {

         f = true;

         for(int i = ; i < n; i++)

         {

             scanf("%d",&a[i]);

         }

         sort(a,a+n);

         for(int i = n-; i >= ; i--)

         {

             if(a[i-] + a[i-] > a[i])

             {

                 f = ;

                 printf("%d\n",a[i-]+a[i-]+a[i]);

                 break;

             }

         }

         if(f)   puts("-1");

     }

     return ;

 }