import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
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();
		sc.close();
		List<Integer> ary = new ArrayList<>();
		int flg = 1;
		while(flg <= A || flg <= B){
			if(A%flg==0&&B%flg==0) {
				ary.add(flg);
			}
			flg++;
		}
		Collections.sort(ary, Collections.reverseOrder());
		System.out.println(ary.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