import java.util.*;

public class Main {
  static int[] list;
    public static void main(String[] args) throws Exception{
      Scanner sc = new Scanner(System.in);
      int a = sc.nextInt();
      int b = sc.nextInt();
      int k = sc.nextInt();
      int cnt = 0;
      for (int i = 100; 1 <= i; i--) {
        if (a%i==0 && b%i==0) {
          cnt++;
          if (cnt == 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