import java.util.Scanner;

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 cnt = 0;
		int ans = 100;

		while (true) {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		}

		System.out.println(ans);

		sc.close();
	}
} import java.util.Scanner; Scanner 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 cnt = 0;
		int ans = 100;

		while (true) {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		}

		System.out.println(ans);

		sc.close();
	}
} 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 cnt = 0;
		int ans = 100;

		while (true) {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		}

		System.out.println(ans);

		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);

		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();

		int cnt = 0;
		int ans = 100;

		while (true) {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		}

		System.out.println(ans);

		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 int cnt = 0; cnt 0 int ans = 100; ans 100 while (true) {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		} true {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		} if (a % ans == 0 && b % ans == 0) {
				cnt++;
			} a % ans == 0 && b % ans == 0 a % ans == 0 a % ans a ans 0 b % ans == 0 b % ans b ans 0 {
				cnt++;
			} cnt++ cnt if (cnt == k) {
				break;
			} cnt == k cnt k {
				break;
			} break; ans-- ans if (ans < 0) {
				break;
			} ans < 0 ans 0 {
				break;
			} break; System.out.println(ans) System.out.println System.out System System.out ans sc.close() sc.close sc String[] args args 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 cnt = 0;
		int ans = 100;

		while (true) {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		}

		System.out.println(ans);

		sc.close();
	}
} 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 cnt = 0;
		int ans = 100;

		while (true) {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		}

		System.out.println(ans);

		sc.close();
	}
} Main
import java.util.Scanner;

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 cnt = 0;
		int ans = 100;

		while (true) {
			if (a % ans == 0 && b % ans == 0) {
				cnt++;
			}
			if (cnt == k) {
				break;
			}
			ans--;
			if (ans < 0) {
				break;
			}
		}

		System.out.println(ans);

		sc.close();
	}
}
