#include <cstdio>
#include <algorithm>
 
using namespace std;
 
const int maxaib=60000;
int aib[60010],v[810],n,i,j,s,sol;
 
int putere(int i)
{
    return i&(-i);
}
 
void aib_update(int i,int s)
{
    for(;i<=maxaib;i+=putere(i)) aib[i]+=s;
}
 
int aib_query(int i)
{
    int sol=0;
    for(;i>0;i-=putere(i)) sol+=aib[i];
    return sol;
}
 
int main()
{
    freopen("nrtri.in", "r", stdin);
    freopen("nrtri.out", "w", stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++) scanf("%d",&v[i]);
    sort(v+1,v+1+n);
    for(i=3;i<=n;i++)
    {
        for(j=1;j<i-1;j++) aib_update(v[j]+v[i-1],1);
        s+=i-2;
        sol+=s-aib_query(v[i]-1);
    }
    printf("%d",sol);
    return 0;
}