you can use both expressions :-)

Hi, what is your difficult in this phrase? I think that it is ok :)

There isn't a rule about this, but because of the use of "sono" in the second part of the sentence, it's more common to skip the first one. The same with the sentence "Appena entrato, è andato in bagno" (and not Appena è entrato, è andato in bagno). This mean Just entered, he's gone to bathroom.