#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;

int v[802];

int caut(int sum,int n,int j){
    int p2=1<<10;
    while(p2>=1){
        if(j+p2<=n && v[j+p2]<=sum){
            j+=p2;
        }
        p2/=2;
    }
    return j;
}
int main()
{
    int n,i,j,nrtri=0,varj;
    FILE*fin,*fout;
    fin=fopen("nrtri.in","r");
    fscanf(fin,"%d",&n);
    for(i=1;i<=n;i++){
        fscanf(fin,"%d",&v[i]);
    }
    fclose(fin);
    sort(v+1,v+n+1);
    for(i=1;i<=n;i++){
        for(j=i+1;j<=n;j++){
            varj=caut(v[i]+v[j],n,j);
            nrtri+=varj-j;
        }
    }
    fout=fopen("nrtri.out","w");
    fprintf(fout,"%d",nrtri);
    fclose(fout);
    return 0;
}