program name
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int32):: n,i,j,l,r,m,now,ans
    integer(int32), allocatable:: a(:)

    read*, n
    allocate(a(n))
    read*, a(:)
    call merge_sort(a,1,n)
    ans=0
    do i=1,n-2
        do j=i+1,n-1
            now = a(i)+a(j)
            l=j
            r=n+1

            do while (r-l > 1)
                m = (l+r)/2
                if (a(m) < now) then
                    l=m
                else
                    r=m
                end if
            end do
            ans=ans+l-j
        end do
    end do
    print'(i0)', ans
contains
    recursive subroutine merge_sort(ar, fst, lst)
        integer(int32),intent(inout):: ar(:)
        integer(int32),intent(in):: fst,lst
        integer(int32):: mdl

        if (lst-fst < 2) then
            if (ar(fst) > ar(lst)) call swap(ar(fst),ar(lst))
            return
        end if

        mdl = (fst+lst)/2
        call merge_sort(ar, fst, mdl)
        call merge_sort(ar, mdl+1, lst)
        call merge_(ar, fst, mdl, lst)
    end subroutine

    subroutine merge_(ar, fst, mdl, lst)
        integer(int32),intent(inout):: ar(:)
        integer(int32),intent(in):: fst, mdl, lst
        integer(int32),allocatable:: tmp(:)
        integer(int32):: li, ri, ti

        allocate(tmp(lst-fst+1))

        li=fst
        ri=mdl+1   
        ti=1

        do while (li <= mdl .and. ri <= lst)
            if (ar(li) <= ar(ri)) then
                tmp(ti) = ar(li)
                li=li+1
            else
                tmp(ti) = ar(ri)
                ri=ri+1
            end if
            ti=ti+1
        end do

        if (li <= mdl) then
            tmp(ti:) = ar(li:mdl)
        else
            tmp(ti:) = ar(ri:lst)
        end if

        ar(fst:lst) = tmp(:)
        deallocate(tmp)
    end subroutine

    subroutine swap(x,y)
        integer(int32),intent(inout):: x,y
        integer(int32):: tmp
        tmp = x
        x = y
        y = tmp
    end subroutine
end program name