import java.util.Scanner;
import java.util.ArrayList;

public class Main {
  public static void main (String[] args) {
    Scanner in = new Scanner(System.in);

    while (in.hasNext()) {
      int A = in.nextInt();
      int B = in.nextInt();
      int K = in.nextInt();

      ArrayList<Integer> commonDivisor = new ArrayList<Integer>();

      for (int i = 1; i <= 100; ++i) {
        if (A % i == 0 && B % i == 0) {
          commonDivisor.add(i);
        } 
      }

      System.out.println(commonDivisor.get(commonDivisor.size() - 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