import java.util.ArrayList;
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();
		List<Integer> list = new ArrayList<Integer>();

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

				}
			}
		}

		System.out.println(list.get(list.size() - K));

	}

}
/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