#include <stdio.h>
#include <stdlib.h>
int v[801];
int main()
{
    FILE *fin, *fout;
    int ras=0,aux,n,i,j,k,st;

    fin=fopen("nrtri.in" , "r" );
    fout=fopen("nrtri.out" , "w" );
    fscanf(fin, "%d" , &n);
    for(i=0; i<n; i++)
        fscanf(fin, "%d"  , &v[i]);
    do
    {
        st=0;
        for( i=0; i+1<n; i++ )
            if( v[i]>v[i+1] )
            {
                aux=v[i];
                v[i]=v[i+1];
                v[i+1]=aux;
                st=1;
            }
    }
    while( st==1 );
    for(i=0; i<n; i++)
    {
        k=i+2;
        for(j=i+1; j<n; j++)
        {
            while(k<=j)
                k++;
            while(k<n && v[i]+v[j]>=v[k])
                k++;
            if(k>j)
                ras=ras+k-j-1;
        }
    }
    fprintf(fout, "%d" , ras);
    fclose(fin);
    fclose(fout);
    return 0;
}