import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);

    int a = sc.nextInt();
    int b = sc.nextInt();
    int k = sc.nextInt();
    int buf = 0;
    int ans = 0;

    for(int i = Math.min(a, b); i > 0; i--){
      if(a % i == 0 && b % i == 0){
        buf += 1;
        if(buf == k){
          ans = i;
          break;
        }
      }
    }

    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