#include<stdio.h>
#include<algorithm>
#define nmax 801
using namespace std;

int a[nmax],n;
int cauta(int st,int dr,int val)
{
    
    int mij=(st+dr)/2;    
    if((a[mij]<=val && a[mij+1]>val) || (a[mij]<=val && mij+1<n))
    return mij;
    else
        if(a[mij]>val)
       return cauta(st,mij,val);
        else 
         if(a[mij]<=val && a[mij+1]<=val)
       return cauta(mij+1,dr,val);

}

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    
    int solfin=0,i,j;

    scanf("%d",&n);
    
    for(i=1; i<=n; ++i)
    scanf("%d",&a[i]);
    
    sort(a+1,a+1+n);
    
    a[n+1]=a[n+2]=50000; //mult
    int m=n-1,poz;
    
    for(i=1; i<m; ++i)    
     for(j=i+1; j<=m; ++j){
             poz=cauta(1,n+1,a[i]+a[j]);
             if(poz!=j)
             solfin+=poz-i-1;
             }
    
    printf("%d\n",solfin);
    
    return 0;
}