import java.util.Arrays;
import java.util.Scanner;
public class Main {
	static int A,B,C;
	//static String ans;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		A=sc.nextInt();
		B=sc.nextInt();

		C=sc.nextInt();
		int a[]=new int[101];
		for(int i=1;i<=100;i++) {
			if(A%i==0&&B%i==0)a[i]=i;
		}
		Arrays.sort(a);
		System.out.println(a[101-C]);
	}
}

/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