import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        
        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;
                }
            }
        }
        
        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 = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        
        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;
                }
            }
        }
        
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        
        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;
                }
            }
        }
        
        System.out.println(ans);
    } main {
        
        Scanner sc = new Scanner(System.in);
        
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        
        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;
                }
            }
        }
        
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = Integer.parseInt(sc.next()); a Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int b = Integer.parseInt(sc.next()); b Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int k = Integer.parseInt(sc.next()); k Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next 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;
                }
            }
        } 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;
                }
            }
        } {
            if((a%i == 0) && (b%i == 0)){
                count++;
                if(count == k){
                    ans = i;
                }
            }
        } if((a%i == 0) && (b%i == 0)){
                count++;
                if(count == k){
                    ans = i;
                }
            } (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){
                    ans = i;
                }
            } count++ count if(count == k){
                    ans = i;
                } count == k count k {
                    ans = i;
                } ans = i ans i 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 = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        
        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;
                }
            }
        }
        
        System.out.println(ans);
    }
} public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        
        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;
                }
            }
        }
        
        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 = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        
        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;
                }
            }
        }
        
        System.out.println(ans);
    }
}