#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
int v[850],n,i,j,k,sum=0,mod=0,x;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int binary(int st, int dr,int x)
{
    int m=(st+dr)/2;
    while(st<=dr)
    {
        m=(st+dr)/2;
        if(v[m]<=x)
            st=m+1;
        else dr=m-1;
    }
    m=(st+dr)/2;
    if(v[m+1]>x) return 1;
    else return 0;

}
int main()
{
    in.sync_with_stdio(false);
    out.sync_with_stdio(false);
    in>>n;
    for(i=0;i<n;i++)
        in>>v[i];
    sort(v,v+n);
    for(i=0;i<n-1;i++)
        for(j=i+1;j<n;j++)
        {
            sum=v[i]+v[j];
            if(binary(j+1,n-1,sum)) mod++;
        }
    out<<mod;
    return 0;
}