import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

/**
 *
 * @author kouki
 */
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();
        List<Integer> list = new ArrayList<>();
        if (A > B) {
            for (int i = 1; i < B+1; i++) {
                if (B % i == 0 && A % i == 0) {
                    list.add(i);
                }
            }
        } else if (B > A) {
            for (int i = 1; i < A+1; i++) {
                if (A % i == 0 && B % i == 0) {
                    list.add(i);
                }
            }
        } else if (A == B) {
            for (int i = 1; i < A+1; i++) {
                if (A % i == 0 && B % i == 0) {
                    list.add(i);
                }
            }
        } else {
        }
        Collections.sort(list, Collections.reverseOrder());
        System.out.println(list.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