var nr:int64;
    n,i,j:longint;
    f1,f2:text;
    a,v,x:array[1..14000] of longint;
begin
        assign(f1,'medie.in');
        reset(f1);
        assign(f2,'medie.out');
        rewrite(f2);
        read(f1,n);
        for i:=1 to n do
        begin
                read(f1,a[i]);
                inc(x[a[i]]);
        end;
        for i:=1 to n-1 do
                for j:=i+1 to n do
                        inc(v[a[i]+a[j]]);
        for i:=1 to n do
                nr:=nr+v[2*a[i]];
        for i:=1 to n do
                nr:=nr-x[a[i]]+1;
        writeln(f2,nr);
        close(f1);
        close(f2);
end.