import java.util.Scanner;

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 ans = 0;
		for(int i = Math.min(A, B); i >= 0; i--) {
			if(A % i == 0 && B % i == 0) {
				K--;
				if(K == 0) {
					ans = i;
					break;
				}
			}
		}
		System.out.println(ans);
	}
}
/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