import java.io.IOException;
import java.util.Arrays;
import java.util.Locale;
import java.util.Scanner;

public class Program {



    public void start() throws IOException {

        Scanner sc = new Scanner(System.in);

        while(sc.hasNext()){

            int numberOfFrontSprockets = sc.nextInt();
            if (numberOfFrontSprockets == 0) System.exit(0);
            int numberOfRearSprockets = sc.nextInt();

            int[] frontTeeth = new int[numberOfFrontSprockets];
            int[] rearTeeth = new int[numberOfRearSprockets];

            for(int i = 0; i < numberOfFrontSprockets; i++){
                frontTeeth[i] = sc.nextInt();
            }

            for(int i = 0; i < numberOfRearSprockets; i++){
                rearTeeth[i] = sc.nextInt();
            }

            int totalNumberOfSprockets = numberOfFrontSprockets * numberOfRearSprockets;
            double[] spread = new double[totalNumberOfSprockets];
            int spreadCounter = 0;

            for(int i = 0; i < numberOfFrontSprockets; i++){
                for(int j = 0; j < numberOfRearSprockets; j++){
                    double spreadValue = ((double) rearTeeth[j]) / ((double) frontTeeth[i]);
                    spread[spreadCounter] = spreadValue;
                    spreadCounter++;
                }
            }

            Arrays.sort(spread);

            double maxSpread = 0;
            for(int i = 0; i < spread.length - 1; i++){
                maxSpread = (spread[i+1] / spread[i]) > maxSpread ? (spread[i+1] / spread[i]) : maxSpread;
            }

            Locale.setDefault(Locale.US);
            System.out.printf("%.2f%n", maxSpread);

        }

    }
}