import java.util.Scanner;

public class Main {

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

/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