import java.util.*;

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 count = 0;
        int ans = 1;
        for (int i = 100; i > 0; i--) {
            if (A % i == 0 && B % i == 0) {
                count++;
                if (count == 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