import java.util.Scanner;
class Main{
    public static void main(String[] args) {
        //入力
        Scanner scn=new Scanner(System.in);
        int a=scn.nextInt();
        int b=scn.nextInt();
        int k=scn.nextInt();
        //処理
        int cnt=0;
        int answer=0;
        for(int i=1;i<=Math.max(a,b);i++){
            if(a%i==0&&b%i==0)cnt++;
        }
        int length=cnt;
        cnt=0;
        for(int i=1;;i++){
            if(a%i==0&&b%i==0)cnt++;
            if(cnt==length-k+1){
                answer=i;
                break;
            }
        }
        //出力
        System.out.println(answer);
    }
}
/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