import java.util.*;
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();
		
		int max = a;
		if( a < b ) {
			max = b;
		}
		int flag = 0;
		for(int i = max; i > 0; i--) {
			if( a%i == 0 && b%i == 0 ) {
				flag++;
			}
			if(flag == 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