import java.util.Scanner;
class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        int num1 = sc.nextInt();
        int num2 = sc.nextInt();
        int order = sc.nextInt();

        int cnt = 0, div = Math.min(num1, num2) + 1;
        while(cnt < order){
            div--;
            if(num1 % div == 0 && num2 % div == 0){
                cnt++;
            }
        }
        System.out.println(div);
    }
}
/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