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[] ans = new int[101];
    for(int i=1; i<=100; i++){
      if( a%i == 0) ans[i]++;
      if( b%i == 0) ans[i]++;
    }
    int kb = 0;
    for(int i=100; i>=1; i--){
      if( ans[i] == 2 ) {
        ++kb;
        if( kb == k){
          System.out.println(i);
          System.exit(0);
        }
      }
    }
  }
}
/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