import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int count = 0;
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        sc.close();
        for(int i=a;i>=1;i--){
            if(a%i == 0 && b%i==0){
                count++;
            }
            if(count==k){
                System.out.println(i);
                return;
            }
        }
        
    }
    
}
/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