#include<cstdio>
#include<algorithm>

using namespace std;

int v[801],i,j,n,k,st,dr,mid;

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+n+1);
        for(i=1;i<=n-2;i++)
                for(j=i+1;j<=n-1;j++)
                {       st=j+1;dr=n;
                        while(st<=dr)
                        {       mid=(st+dr)/2;
                                if(v[i]+v[j]<=v[mid]) {k++;st=mid+1;}
                                else    dr=mid-1;
                        }
                }
        printf("%d\n",k);
        return 0;
}