import java.util.Arrays;
import java.util.Scanner;


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

        int A = sc.nextInt();
        int B = sc.nextInt();
        int Q = sc.nextInt();
        
        int[] ans = new int[101];
        
        for(int i = 100;i > 0 ; i--) {
        	if((A%i==0) && (B%i==0)) {
        		ans[i] = i;
        	}
        }
        Arrays.sort(ans);
        System.out.println(ans[101-Q]);
    }
}
/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