#include<stdio.h>
#include<algorithm>
using namespace std;
int main()
{
    int n,i,v[1001],j,nr=0,k;
    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-1;i++)
        for(j=i+1;j<n;j++)
            for(k=j+1;k<=n;k++)
                if(v[k]-v[j]<v[i])
                    nr++;
                else
                    break;
    printf("%d",nr);
    return 0;
}