tsls function help

Hi,

I need help. I need to use tsls function on my simultaneous model.

This is my model:

Ct=a0+a1Yt+a2Ct-1+ut1
Yt=b0+b1It+b2Mt+ut2
It=c0+c1rt+c2It-1+ut3
Gt=Yt-Ct-It


How to use tsls on this model, please?

Thank you for your help.

Lado