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[] surp = new int[Math.min(a,b)+1];
      for(int i = 1;i <= Math.min(a,b);i++){
      	if(a%i == 0 && b%i == 0){
        surp[i] = i;
        }
      }
      Arrays.sort(surp);
      System.out.println(surp[Math.min(a,b)-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