import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        
        Scanner scanner = new Scanner(System.in);
        int A = scanner.nextInt();
        int B = scanner.nextInt();
        int K = scanner.nextInt();
        int count = 0;
        
        List<Integer> list = new ArrayList<Integer>();
        for(int i=1; i<=100; i++){
            if(A%i==0 && B%i==0){
                list.add(i);
                count++;
            }
        }
        
        Collections.sort(list, 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