#include<fstream>
#include<algorithm>
using namespace std;
int v[801];
int n,i,st,dr,p,s,mid,sum,j;


ifstream fin ("nrtri.in");
ofstream fout ("nrtri.out");

int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n;i++)
        for(j=i+1;j<=n;j++)
    {
        p=0;
        s=v[i]+v[j];
        st=j;
        dr=n;
        while(st<=dr){
            mid=(st+dr)/2;
        if(st<v[mid])
            dr=mid-1;
        else
        {st=mid+1;
         p=mid;}
        }
    if(p!=0)
        sum=sum+p-j;
            }
    fout<<s;

    return 0;
}