import java.util.*;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    // 入力を取得
    int a = sc.nextInt();
    int b = sc.nextInt();
    int k = sc.nextInt();

    ArrayList<Integer> divisor  = new ArrayList<Integer>();
    for(int i= a;i>0;i--){
      if(a%i==0 && b%i==0){
        divisor.add(i);
      }
    }

    // 出力
    System.out.println(divisor.get(k-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