Fortigate 60D 2 interfaces WAN HA

[fethi113]

hi, 

I recently install and Configure my Fortigate 60D with FortiOS 5.0

my architecture consists of two WAN interfaces WAN1 and WAN2 and I have two LAN: LAN 1 and LAN 2

LAN 1 ----> WAN 1 "ADSL" ----> Internet LAN 2 ----> WAN 2 "ADSL" ----> Internet

I installed a fiber optic line to the Internet "WAN 3"

need:

1 => shared WAN 3 LAN 1 and LAN 2 2 => there is a LAN 3 "connection to the CISCO router to establish LAN connection between Cisco and Fortigate but there is a rule to establish the routing optical fiber Internet connection When I substituted with one exmple WAN WAN 3 I lost the connection between the LAN 1 and 2 "NATs"

thank you for advanced :)