//package abc120_B;

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;
		for (int i = 100; i > 0; 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) {
		
		Scanner sc = new Scanner(System.in);
		
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		
		int cnt = 0;
		for (int i = 100; i > 0; i--) {
			if (a % i == 0 && b % i == 0) cnt++;
			if (cnt == k) {
				System.out.println(i);
				return;
			}
		}
	}

} 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;
		for (int i = 100; i > 0; 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();
		
		int cnt = 0;
		for (int i = 100; i > 0; 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 int cnt = 0; cnt 0 for (int i = 100; i > 0; i--) {
			if (a % i == 0 && b % i == 0) cnt++;
			if (cnt == k) {
				System.out.println(i);
				return;
			}
		} int i = 100; int i = 100; i 100 i > 0 i 0 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++; a % i == 0 && b % i == 0 a % i == 0 a % i a i 0 b % i == 0 b % i b i 0 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) {
		
		Scanner sc = new Scanner(System.in);
		
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		
		int cnt = 0;
		for (int i = 100; i > 0; 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) {
		
		Scanner sc = new Scanner(System.in);
		
		int a = sc.nextInt();
		int b = sc.nextInt();
		int k = sc.nextInt();
		
		int cnt = 0;
		for (int i = 100; i > 0; i--) {
			if (a % i == 0 && b % i == 0) cnt++;
			if (cnt == k) {
				System.out.println(i);
				return;
			}
		}
	}

} Main
//package abc120_B;

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;
		for (int i = 100; i > 0; i--) {
			if (a % i == 0 && b % i == 0) cnt++;
			if (cnt == k) {
				System.out.println(i);
				return;
			}
		}
	}

}