program exam_and_wizard
  implicit none
  integer :: n, i, j, tot, num
  integer :: a(100000), b(100000), c(100000)
  a = 0
  b = 0
  c = 0
  read(*,*) n
  read(*,*) a(1:n)
  read(*,*) b(1:n)
  c(1:n) = a(1:n) - b(1:n)
  num = 0
  tot = 0
  do i = 1, n
    if (c(i).lt.0) then
      num = num + 1
      tot = tot - c(i)
    end if
  end do
  if (num.eq.0) then
    write(*,'(i0)') 0
    stop
  end if
  call merge_sort(n,c(1:n))
  do i = n, 1, -1
    if (c(i).lt.0) exit
    tot = tot - c(i)
    num = num + 1
    if (tot.le.0) then
      write(*,'(i0)') num
      stop
    end if
  end do
  write(*,'(i0)') -1
  stop
contains
  subroutine merge_sort(n,c)
    implicit none
    integer, intent(in) :: n
    integer, intent(inout) :: c(n)
    integer :: num, lth, ubd, i
    num = n
    lth = 1
    do while (num.gt.1)
      do i = 1, num/2
        ubd = min(2*i*lth,n)
        call merge(c(2*(i-1)*lth+1:(2*i-1)*lth),c((2*i-1)*lth+1:ubd))
      end do
      lth = 2*lth
      num = (num+1)/2
    end do
    return
  end subroutine merge_sort
  subroutine merge(c1,c2)
    implicit none
    integer, intent(inout) :: c1(:), c2(:)
    integer :: c(size(c1)+size(c2))
    integer :: i1, i2, n1, n2
    i1 = 1
    i2 = 1
    n1 = size(c1)
    n2 = size(c2)
    do while (i1.le.n1.and.i2.le.n2)
      if (c1(i1).le.c2(i2)) then
        c(i1+i2-1) = c1(i1)
        i1 = i1+1
      else
        c(i1+i2-1) = c2(i2)
        i2 = i2+1
      end if
    end do
    if (i1.le.n1) then
      c(i1+i2-1:n1+n2) = c1(i1:n1)
    else if (i2.le.n2) then
      c(i1+i2-1:n1+n2) = c2(i2:n2)
    end if
    c1 = c(1:n1)
    c2 = c(n1+1:n1+n2)
    return
  end subroutine merge
end program exam_and_wizard