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();
        List<Integer> list = new ArrayList<>();
        int min = Math.min(a,b);
        for (int i = 1; i<=min;i++) {
            if (a % i == 0 && b % i == 0) list.add(i);
        }
        list.sort(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