
import java.util.Arrays;
import java.util.Collections;
import java.util.Scanner;
//abc120b
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 smaller =Math.min(a, b);
		Integer[] divisors =new Integer[smaller+1];
		for (int i=0;i<=smaller;i++) {
			divisors[i] =0;
		}
		for (int i=1;i<=smaller;i++) {
			if (a%i==0&&b%i==0) {
				divisors [i] += i;
			}
		}
		Arrays.sort(divisors, Collections.reverseOrder());
		System.out.println(divisors[k-1]);
//━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
	}
	//----------------------------------------
	//置き場
	
	//----------------------------------------
}
/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