import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt(), b = sc.nextInt();
		int k = sc.nextInt();
		for (int i = Math.min(a, b); i >= 1; i--) {
			if(a%i==0&&b%i==0) {
				if(k==1) {
					System.out.println(i);
					break;
				}else {
					k--;
				}
			}
		}
		sc.close();
	}
}
/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