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();
        int[] n = new int[100];
 
        int min = Math.min(a, b);
        int cnt = 0;
        for (int i = 1; i <= min; i++) {
            if (a % i == 0 && b % i == 0)
                n[cnt++] = i;
            else
                continue;
        }
        
        System.out.println(n[cnt - k]);
    }
}
/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