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;
		for(int i=100;i>=1;i--) {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==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 count =0;
		for(int i=100;i>=1;i--) {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==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 count =0;
		for(int i=100;i>=1;i--) {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==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 count =0;
		for(int i=100;i>=1;i--) {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==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 count =0; count 0 for(int i=100;i>=1;i--) {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==K) {
					System.out.println(i);
					return ;
				}
			}
		} int i=100; int i=100; i 100 i>=1 i 1 i-- i-- i {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==K) {
					System.out.println(i);
					return ;
				}
			}
		} {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==K) {
					System.out.println(i);
					return ;
				}
			}
		} if (A%i==0&&B%i==0) {
				count ++;
				if (count ==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 {
				count ++;
				if (count ==K) {
					System.out.println(i);
					return ;
				}
			} count ++ count if (count ==K) {
					System.out.println(i);
					return ;
				} count ==K count 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 count =0;
		for(int i=100;i>=1;i--) {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==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 count =0;
		for(int i=100;i>=1;i--) {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==K) {
					System.out.println(i);
					return ;
				}
			}
		}
	}
} 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;
		for(int i=100;i>=1;i--) {
			if (A%i==0&&B%i==0) {
				count ++;
				if (count ==K) {
					System.out.println(i);
					return ;
				}
			}
		}
	}
}