See the Integer class and the static parseInt() method:
http://developer.android.com/reference/java/lang/Integer.html
Integer.parseInt(et.getText().toString());
You will need to catch NumberFormatException though in case of problems whilst parsing, so:
int myNum = 0;
try {
myNum = Integer.parseInt(et.getText().toString());
} catch(NumberFormatException nfe) {
System.out.println("Could not parse " + nfe);
}