import java.util.*;

public class festas {
    public static void main( String[] args ){
        Scanner s = new Scanner(System.in);
        int DA = s.nextInt(), MA = s.nextInt();
        int DB = s.nextInt(), MB = s.nextInt();
        s.close();
        if (MA < MB || (MA == MB && DA < DB))
            System.out.println("A");
        else
            System.out.println("B");
    }
}