
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 ans = 0;
		for(int i = 100; i > 0; i--) {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		}
		System.out.println(ans);
	}

} 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 ans = 0;
		for(int i = 100; i > 0; i--) {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		}
		System.out.println(ans);
	}

} 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 ans = 0;
		for(int i = 100; i > 0; i--) {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		}
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		int K = sc.nextInt();
		int count = 0;
		int ans = 0;
		for(int i = 100; i > 0; i--) {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		}
		System.out.println(ans);
	} 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 ans = 0; ans 0 for(int i = 100; i > 0; i--) {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		} int i = 100; int i = 100; i 100 i > 0 i 0 i-- i-- i {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		} {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		} if((A % i == 0) && (B % i == 0)) {
				count++;
			} (A % i == 0) && (B % i == 0) (A % i == 0) A % i A i 0 (B % i == 0) B % i B i 0 {
				count++;
			} count++ count if(count == K) {
				ans = i;
				break;
			} count == K count K {
				ans = i;
				break;
			} ans = i ans i break; System.out.println(ans) System.out.println System.out System System.out ans 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 ans = 0;
		for(int i = 100; i > 0; i--) {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		}
		System.out.println(ans);
	}

} 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 ans = 0;
		for(int i = 100; i > 0; i--) {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		}
		System.out.println(ans);
	}

} 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 ans = 0;
		for(int i = 100; i > 0; i--) {
			if((A % i == 0) && (B % i == 0)) {
				count++;
			}
			if(count == K) {
				ans = i;
				break;
			}
		}
		System.out.println(ans);
	}

}
