import java.util.*;
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 gcd = gcd(a, b);

      for(int i = gcd; i >= 1; i--) {
        if(a % i == 0 && b % i == 0) {
          k--;
          if(k == 0) {
            System.out.println(i);
            return;
          }
        }
      }
  }

  private static int gcd(int a, int b) {
    if(b == 0)
      return a;
    return gcd(b, a % b);
  }
}
/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