#include<algorithm>
using namespace std;
int a[805],k,n;
int cbin (int st,int dr,int s)
{
    int mij,sol=st-1;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(s>=a[mij])
            st=mij+1,sol=mij;
        else
            dr=mij-1;
    }
    return sol;
}
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int i,j,l;
    scanf("%d",&n);
    for(i=1;i<=n;++i)
        scanf("%d",&a[i]);
    sort(1+a,n+a+1);
    for(i=1;i<=n-2;++i)
        for(j=i+1;j<=n-1;++j)
                k+=cbin(j+1,n,a[i]+a[j])-j;
    printf("%d",k);
    return 0;
}