program main
  implicit none
  integer*8::L,H,up,i,j,bad
  integer*8,allocatable::dp(:),dp2(:)
  read *,L,H
  up = INT(SQRT(DBLE(H)))
  allocate(dp(up),dp2(L:H))
  dp  = 0
  dp2 = 0
  bad = 1
  do i=2,up
     if(dp(i).ne.0) cycle
     do j=i+i,up,i
        dp(j) = 1
     end do

     do j=((L+i-1)/i)*i,H,i
        if(dp2(j).ne.0) cycle
        dp2(j) = 1
        bad    = j
     end do
  end do

  print'(i0)',bad
end program main