#include <cstdio>
#include <algorithm>
using namespace std;

    int n;
    int v[805];
int bisearch(int val)
{
    int i,step;
    for(step=1;step <= n;step <<=1);
    for(i=0;step;step >>= 1)
        if((i | step) <= n && v[i|step] <= val)
            i|=step;
    return i;
}
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    int i,j,k;
    long long sol = 0;
    for(i=1;i<=n;++i)
        scanf("%d",&v[i]);
    sort(&v[1],&v[n+1]);
    for(i=1;i<n;++i)
    {
        for(j=i+1;j<=n;++j)
        {
            k = bisearch(v[i] + v[j]);
            if(k)
                sol += k-j;
        }
    }
    printf("%lld\n",sol);
    return 0;
}