import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        
        int count = 0;
        int ans = 0;
        for(int i = 100; i > 0; i--){
            if((a%i == 0) && (b%i == 0)){
                count++;
                if(count == k){
                    ans = i;
                }
            }
        }
        
        System.out.println(ans);
    }
}
/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