import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
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();

		int max = a > b ? a : b;
		List<Integer> list = new ArrayList<Integer>();

		for (int i = 1; i <= max; i++) {

			if (a % i == 0 && b % i == 0) {
				list.add(i);
			}

		}

		Collections.sort(list);
		Collections.reverse(list);

		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