connecting 3 sites via one tunel

RouterOS Forwarding Protocols
1

Dear Colleagues,

I am new with Mikrotik and I need information about how connect 3 sites which are set up as follow :

The Sites I need to connect are :

In AR (I am here)

Site A, Corporate Office
Site B, Branch Office

In US

Site C, Remote Corporate Office.

I have :

  1. Site A (Corporate AR) connected to Site C (in US) via MPLS connection with a Cisco router which is not managed by me. Working since years.

  2. Site A " connected to Site B (Branch in AR) connected via IPsec with two new Mikrotiks RB450G in each peer. Working since a week.

I need :

  1. Coonect Site B (Branch in AR) with Site C (in US) passing thru the IPsec tunel already made between A & B.

I hope this can be understand.

Thanks in advance!