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 count = 0;
		int n = 0;

		for (int i = Math.max(a, b); i >= 1; i--) {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		}

		System.out.println(n);
	}
} 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 count = 0;
		int n = 0;

		for (int i = Math.max(a, b); i >= 1; i--) {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		}

		System.out.println(n);
	}
} 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 count = 0;
		int n = 0;

		for (int i = Math.max(a, b); i >= 1; i--) {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		}

		System.out.println(n);
	} main {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();

		int count = 0;
		int n = 0;

		for (int i = Math.max(a, b); i >= 1; i--) {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		}

		System.out.println(n);
	} 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 count = 0; count 0 int n = 0; n 0 for (int i = Math.max(a, b); i >= 1; i--) {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		} int i = Math.max(a, b); int i = Math.max(a, b); i Math.max(a, b) Math.max Math a b i >= 1 i 1 i-- i-- i {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		} {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		} if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			} a % i == 0 && b % i == 0 a % i == 0 a % i a i 0 b % i == 0 b % i b i 0 {
				count++;
				n = i;
				if (count >= k) break;
			} count++ count n = i n i if (count >= k) break; count >= k count k break; System.out.println(n) System.out.println System.out System System.out n 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 count = 0;
		int n = 0;

		for (int i = Math.max(a, b); i >= 1; i--) {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		}

		System.out.println(n);
	}
} 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 count = 0;
		int n = 0;

		for (int i = Math.max(a, b); i >= 1; i--) {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		}

		System.out.println(n);
	}
} 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 count = 0;
		int n = 0;

		for (int i = Math.max(a, b); i >= 1; i--) {
			if (a % i == 0 && b % i == 0) {
				count++;
				n = i;
				if (count >= k) break;
			}
		}

		System.out.println(n);
	}
}
