#include<fstream>
#include<algorithm>
#define maxn 805
using namespace std;
ifstream fi("nrtri.in");
ofstream fo("nrtri.out");

int i,j,k,n,s=0;
int a[maxn],x;

int bsearch1(int x,int st,int dr){
    int mijl;
     
    while(st<dr){
                 mijl=(st+dr)/2;
                 if(a[mijl]<=x) st=mijl+1;
                 else dr=mijl;
                }
                 
    mijl=(st+dr)/2;
    if(a[mijl]>x) mijl--;
    return mijl;
}

int main(){
    fi>>n;
    for(i=1;i<=n;i++) fi>>a[i];
    
    sort(a+1,a+n+1);
    
    for(i=1;i<=n-2;i++)
      {
       for(j=i+1;j<=n-1;j++){
                             x=a[i]+a[j];
                             k=bsearch1(x,j+1,n);
                             if(a[k]<=x) s+=(k-j);
                            }                 
      }
    
    fo<<s;
    
    fi.close();
    fo.close();
    return 0;
}