import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args){
        FastScanner fs = new FastScanner();
        PrintWriter pw = new PrintWriter(System.out);

        int a = fs.nextInt();
        int b = fs.nextInt();
        int k = fs.nextInt();
        int l = Math.min(a, b);
        int kk = 0;
        while(true){
            if(a % l == 0 && b % l == 0){
                kk++;
            }
            if(kk >= k){
                break;
            }
            l--;
        }
        pw.println(l);
        pw.flush();
    }

    static int gcd(int a, int b) {
        return b > 0 ? gcd(b, a % b) : a;
    }

    public static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner(Reader in) {
            br = new BufferedReader(in);
        }

        public FastScanner() {
            this(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String readNextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}

/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