#include<fstream>
#include<algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,v[803],i,j,st,dr,mid,sol;
int main(){
fin>>n;
for(i=1;i<=n;i++){
    fin>>v[i];
}
sol=0;
sort(v+1,v+n+1);
for(i=1;i<=n;i++){
    for(j=i+1;j<=n;j++){
        st=j+1;
        dr=n;
        while(st<=dr){
            mid=(st+dr)/2;
            if(v[mid]>v[i]+v[j]){
                dr=mid-1;
            }
            if(v[mid]<=v[i]+v[j]){
                st=mid+1;
            }
        }
        sol=sol+dr-j;
    }
}
fout<<sol;
return 0;
}