import java.util.Scanner;

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

        // Read input
        String parent1 = scanner.nextLine();
        String parent2 = scanner.nextLine();
        int splitPoint = scanner.nextInt();

        // Perform crossover
        String child1 = parent1.substring(0, splitPoint) + parent2.substring(splitPoint);
        String child2 = parent2.substring(0, splitPoint) + parent1.substring(splitPoint);

        // Calculate fitness levels
        double child1Fitness = calculateFitness(child1);
        double child2Fitness = calculateFitness(child2);

        // Determine the surviving child
        String survivor = (child1Fitness >= child2Fitness) ? child1 : child2;

        // Check if mutation is required
        if (calculateFitness(survivor) < 0.5) {
            survivor = flipBits(survivor);
        }

        // Print the surviving child
        System.out.println(survivor);
    }

    private static double calculateFitness(String bitString) {
        int onesCount = 0;
        for (char bit : bitString.toCharArray()) {
            if (bit == '1') {
                onesCount++;
            }
        }
        return (double) onesCount / bitString.length();
    }

    private static String flipBits(String bitString) {
        StringBuilder flipped = new StringBuilder();
        for (char bit : bitString.toCharArray()) {
            flipped.append((bit == '0') ? '1' : '0');
        }
        return flipped.toString();
    }
}