import java.util.ArrayList;
import java.util.Scanner;

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();
		ArrayList<Integer> d=new ArrayList<Integer>();
		for(int i=Math.max(A, B);i>=1;i--){
			if(A%i==0 && B%i==0) d.add(i);
		}
		//d.forEach(e->System.out.println(e));
		System.out.println(d.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