import java.util.ArrayList;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int A = sc.nextInt();
        int B = sc.nextInt();
        int K = sc.nextInt();
        ArrayList<Integer> commonDivisors = new ArrayList<>();
        int idx = Math.min(A, B);

        for (int i = idx; i > 0; i--) {
            if (A % i == 0 && B % i == 0) {
                commonDivisors.add(i);
                if (commonDivisors.size() == K) {
                    break;
                }
            }
        }

        System.out.println(commonDivisors.get(K - 1));
    }

}




/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz