#include <stdio.h>
#include <algorithm>
#define lim 800
using namespace std;
int v[lim+1];
int main(){
    FILE *fin,*fout;
    fin=fopen("nrtri.in","r");
    fout=fopen("nrtri.out","w");
    int i,j,k,n,cate=0;
    fscanf(fin,"%d",&n);
    for(i=1;i<=n;i++)
        fscanf(fin,"%d",&v[i]);
    sort(v+1,v+n+1);
    for(i=1;i<n;i++){
        k=i+1;
        for(j=i+1;j<n;j++){
            while(k<=n and v[i]+v[j] >= v[k])
                k++;
            if(k  >j)
                cate += k-j-1;
        }
    }
    fprintf(fout,"%d",cate);
    fclose(fin);
    fclose(fout);
    return 0;
}