i have three Activities A , B  and C ; 
The Activity C above the activity B and B above A . 
class A : 
button.setonclicklistener...
.
.
.{
startactivity(A.this , B.class() )  ;
}
.
.
.}
class B :
button.setonclicklistener...
.
.
.{
startactivity(B.this , C.class() )  ;
}
.
.
.}
now I'm in Activity C , how delete (finish)the Activity C , and B with a Button From activity C  : 
button.setonclicklistener...
.
.
.{
Finish();//activity C 
Finish();//activity B 
}
.
.
.}