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

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		Long A = Long.parseLong(sc.next());
		Long B = Long.parseLong(sc.next());
		int K = Integer.parseInt(sc.next());
		sc.close();
		ArrayList<Integer> list = new ArrayList<Integer>();

		for(int i = 1; i <= 100 ; i++) {
			if(A % i == 0 && B % i == 0) {
				list.add(i);
			}
		}
		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