#include<cstdio>
#include<algorithm>
using namespace std;
int n,i,j,k,p,ct=0,v[810];
int cautbin(int val)
{
    int start=0;int step=(1<<10);
    for(;step;step>>=1)
    {
        int index=start+step;
        if(index>n) continue;
        if(v[index]<=val) start=step;
    }return start;
}
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++)
    {
        k=v[i]+v[j];
        p=cautbin(k);
        if(p==i || p==j) continue;
        if(k>=v[p]) ct=ct+p-j;
    }
    printf("%d",ct);
}