03. Stream Of Letters - with append()

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        String command = scanner.nextLine();

        boolean isCFound = false;
        boolean isOFound = false;
        boolean isNFound = false;

        StringBuilder sb = new StringBuilder();

        while (!"End".equals(command)) {

            char letter = command.charAt(0);
            if (letter < 'A' || (letter > 'Z' && letter < 'a') || letter > 'z') {
                command = scanner.nextLine();
                continue;
            }

            if ("c".equals(command) && !isCFound) {
                isCFound = true;
            } else if ("o".equals(command) && !isOFound) {
                isOFound = true;
            } else if ("n".equals(command) && !isNFound) {
                isNFound = true;
            } else {
                sb.append(command);
            }
            if (isCFound && isOFound && isNFound) {
                System.out.print(sb.append(" "));
                isCFound = false;
                isOFound = false;
                isNFound = false;
                sb.setLength(0);
            }
            command = scanner.nextLine();
        }
    }
}