How can I fix this if-then structure to break out of the loop as needed?

The problem I seek to solve is a game of cups. The user enters a string with no spaces of a series of connected A's, B's, and C's. An example is "AB" or "ABBBCABA". The game is that the player moves the cup of the letter selected. The prize begins in position 1, or the leftmost cup. Here is a picture that helps visualize the movements.

movement picture

An example move entered "AB" should output 3. An example move of "BC" should output 3.

My code is giving incorrect numbers but I can't figure out where I went wrong logically.

import java.io.*;

public class trik {

    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String s = reader.readLine();
        int position = 1;
        if (s.length() == 1) { // A
            if (s.contains("A")) {
                System.out.println(2);
            }
            if (s.contains("B")) {
                System.out.println(1);
            }
            if (s.contains("C")) {
                System.out.println(3);
            }
        } else {
            String[] parts = s.split("");
            int i = 0;
            while (i < parts.length) {
                if (parts[i].equals("A")) {
                    if (position != 3) {
                        if (position == 1) {
                            position = 2;
                        }
                        if (position == 2) {
                            position = 1;
                        }
                    }
                }
                if (parts[i].equals("B")) {
                    if (position != 1) {
                        if (position == 2) {
                            position = 3;
                        }
                        if (position == 3) {
                            position = 2;
                        }
                    }
                }
                if (parts[i].equals("C")) {
                    if (position != 2) {
                        if (position == 1) {
                            position = 3;
                        }
                        if (position == 3) {
                            position = 1;
                        }
                    }
                }
                i++;
            }
            System.out.println(position);

        }

    }
}