import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int A, B, K;
		A = sc.nextInt();
		B = sc.nextInt();
		K = sc.nextInt();
		sc.close();
		int a = 0;
		int ans = 0;
		for (int i = 100; i >= 1; i--) {
			if (A % i == 0 && B % i == 0) {
				a++;
				if (a == K) {
					ans = i;
				}
			}
		}
		System.out.println(ans);
	}
}

/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