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(), k = sc.nextInt();
		int [] Array = new int [50];
		int counter = 0;
		for(int i = 1; i <= a && i <= b; i++) {
			if(a % i == 0 && b % i == 0) {
				Array[counter] = i;
				counter++;
			}
		}
		System.out.println(Array[counter - 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