# include <cstdio>
# include <algorithm>
using namespace std;
int n,i,a[1001],j,nr=0;

int cautare(int n, int a[], int st, int dr)
{
    int m,p=0;
    if(st==dr && a[st]<=n) return st;
    else if(st==dr) return st-1;
    else
    {
        while(st<=dr && p==0)
        {
            m=(st+dr)/2;
            if(a[m]==n) p=m;
            else if(a[m]>n) dr=m-1;
            else st=m+1;
        }
        if(p==0) return dr;
        else return p;
    }
}

int main()
{
    freopen("nrtri.in", "r", stdin);
    freopen("nrtri.out", "w", stdout);
    scanf("%d", &n);
    for(i=1; i<=n; ++i) scanf("%d", &a[i]);
    sort(a+1, a+n+1);
    for(i=1; i<=n-2; ++i)
    {
        for(j=i+1; j<=n-1; ++j)
        nr=nr+cautare(a[i]+a[j],a,j+1,n)-j;
    }
    printf("%d", nr);
}