program main
    use iso_fortran_env
    implicit none
    integer(int64) :: ans
    integer(int64) :: n
    integer(int64) :: k, i

    read *, n
    ans = 0

    do k = 1, n
        i = int( n/k )
        ans = ans + k * (i * (i + 1) / 2)
    enddo

    print *, ans

end program main
