import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		sc.close();

		int cnt = 0;
		for (int i = Math.max(a, b); ; i--) {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		}
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		sc.close();

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

		int cnt = 0;
		for (int i = Math.max(a, b); ; i--) {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		}
	} main {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		sc.close();

		int cnt = 0;
		for (int i = Math.max(a, b); ; i--) {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		}
	} 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 sc.close() sc.close sc int cnt = 0; cnt 0 for (int i = Math.max(a, b); ; i--) {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		} int i = Math.max(a, b); int i = Math.max(a, b); i Math.max(a, b) Math.max Math a b i-- i-- i {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		} {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		} if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			} a % i == 0 && b % i == 0 a % i == 0 a % i a i 0 b % i == 0 b % i b i 0 {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			} cnt++ cnt if (cnt == k) {
					System.out.println(i);
					return;
				} cnt == k cnt k {
					System.out.println(i);
					return;
				} System.out.println(i) System.out.println System.out System System.out i return; String[] args args public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		sc.close();

		int cnt = 0;
		for (int i = Math.max(a, b); ; i--) {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		}
	}
} public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		sc.close();

		int cnt = 0;
		for (int i = Math.max(a, b); ; i--) {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		}
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		sc.close();

		int cnt = 0;
		for (int i = Math.max(a, b); ; i--) {
			if (a % i == 0 && b % i == 0) {
				cnt++;
				if (cnt == k) {
					System.out.println(i);
					return;
				}
			}
		}
	}
}
