westbow% cat Demo.java
class Demo {

    public static int pi(int n){
	int a = 0;
	while (n!=0){a=a+1;n=n-2;};
	return a;
    }
    
    public static void main(String[] args){
        int n = Integer.parseInt(args[0], 10);
	int a = pi(n);
	System.out.println(a);
    }
}
westbow% javac Demo.java
westbow% javap -c Demo
Compiled from "Demo.java"
class Demo extends java.lang.Object{
Demo();
  Code:
   0:	aload_0
   1:	invokespecial	#1; //Method java/lang/Object."<init>":()V
   4:	return

public static int pi(int);
  Code:
   0:	iconst_0
   1:	istore_1
   2:	iload_0
   3:	ifeq	17
   6:	iload_1
   7:	iconst_1
   8:	iadd
   9:	istore_1
   10:	iload_0
   11:	iconst_2
   12:	isub
   13:	istore_0
   14:	goto	2
   17:	iload_1
   18:	ireturn

public static void main(java.lang.String[]);
  Code:
   0:	aload_0
   1:	iconst_0
   2:	aaload
   3:	bipush	10
   5:	invokestatic	#2; //Method java/lang/Integer.parseInt:(Ljava/lang/String;I)I
   8:	istore_1
   9:	iload_1
   10:	invokestatic	#3; //Method pi:(I)I
   13:	istore_2
   14:	getstatic	#4; //Field java/lang/System.out:Ljava/io/PrintStream;
   17:	iload_2
   18:	invokevirtual	#5; //Method java/io/PrintStream.println:(I)V
   21:	return

}

westbow% java Demo 246
123
westbow% java Demo 245
% <non-terminating computation aborted with ctrl-C>
westbow%