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 count =0;
		if(A<B){
			for(int i=A;i>=1;i--) {
				if(A%i==0&&B%i==0) {
					count++;
					if(count==K){
						System.out.println(i);
					}
				}
			}
		}
		else if(A>B){
			for(int i=B;i>=1;i--) {
				if(A%i==0&&B%i==0) {
					count++;
					if(count==K){
						System.out.println(i);
					}
				}
			}
		}
		else if(A==B){
			for(int i=A;i>=1;i--) {
				if(A%i==0&&B%i==0) {
					count++;
					if(count==K){
						System.out.println(i);
					}
				}
			}
		}
	}
}

/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