The number of cats on the street is 2/3*300 = <<2/3*300=200>>200
If there are 300 animals on the street, and 200 are cats, there are 300-200 = <<300-200=100>>100 dogs.
Since a dog has four legs, the total number of legs the 100 dogs have is 100*4 = <<100*4=400>>400 legs.
#### 400