import java.util.*;
public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        // 整数の入力
        int a = sc.nextInt();
        int b = sc.nextInt();
        int k = sc.nextInt();
        for(int i=a<b?a:b;i>0;i--){
          if(a%i==0 && b%i==0) k--;
          if(k==0){
             System.out.println(i);
             return;
          }
        }
        // 出力
       
    }
}

/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