import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;
 
public class Main {
    public static void main(String args[]) {
        final Scanner lineScanner = new Scanner(System.in);
        final int A = lineScanner.nextInt();
        final int B = lineScanner.nextInt();
        final int needIndex = lineScanner.nextInt();
 
        List<Integer> numList = new ArrayList<>();
        for (int i = 1; i <= A && i <= B; i++) {
            if (A % i == 0 && B % i == 0) {
                numList.add(i);
            }
        }
        Collections.sort(numList, Collections.reverseOrder());
        System.out.println(numList.get(needIndex - 1));
    }
}
/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