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();
		int min = Math.min(A, B);
		int count = 0;
		int val = 0;
		for(int i=min; i>=1; i--) {
			if(A%i==0 && B%i==0) {
				count++;
				val = i;
				if(count==K) {
					break;
				}
			}
		}
		System.out.println(val);
	}

}
/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