
import java.util.Scanner;

class Main {

	public static void main(String[] args) {
		new Main().exec();
	}

	void exec() {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		for (int i = Math.min(a, b); i >= 1; --i) {
			if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			}
		}
		sc.close();
	}

} import java.util.Scanner; Scanner java.util class Main {

	public static void main(String[] args) {
		new Main().exec();
	}

	void exec() {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		for (int i = Math.min(a, b); i >= 1; --i) {
			if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			}
		}
		sc.close();
	}

} Main public static void main(String[] args) {
		new Main().exec();
	} main {
		new Main().exec();
	} new Main().exec() new Main().exec new Main() String[] args args void exec() {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		for (int i = Math.min(a, b); i >= 1; --i) {
			if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			}
		}
		sc.close();
	} exec {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		for (int i = Math.min(a, b); i >= 1; --i) {
			if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			}
		}
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc int k = sc.nextInt(); k sc.nextInt() sc.nextInt sc for (int i = Math.min(a, b); i >= 1; --i) {
			if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			}
		} int i = Math.min(a, b); int i = Math.min(a, b); i Math.min(a, b) Math.min Math a b i >= 1 i 1 --i --i i {
			if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			}
		} {
			if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			}
		} if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			} a % i == 0 && b % i == 0 a % i == 0 a % i a i 0 b % i == 0 b % i b i 0 {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			} --k k if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				} k == 0 k 0 {
					System.out.println(i);
					sc.close();
					return;
				} System.out.println(i) System.out.println System.out System System.out i sc.close() sc.close sc return; sc.close() sc.close sc

import java.util.Scanner;

class Main {

	public static void main(String[] args) {
		new Main().exec();
	}

	void exec() {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		for (int i = Math.min(a, b); i >= 1; --i) {
			if (a % i == 0 && b % i == 0) {
				--k;
				if (k == 0) {
					System.out.println(i);
					sc.close();
					return;
				}
			}
		}
		sc.close();
	}

}
