import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int count = 0;
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        sc.close();
        for(int i=a;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 count = 0;
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        sc.close();
        for(int i=a;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 count = 0;
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        sc.close();
        for(int i=a;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 count = 0;
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        sc.close();
        for(int i=a;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 count = 0; count 0 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 sc.close() sc.close sc for(int i=a;i>=1;i--){
            if(a%i == 0 && b%i==0){
                count++;
            }
            if(count==k){
                System.out.println(i);
                return;
            }
        } int i=a; int i=a; i a 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++;
            } 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){
                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 count = 0;
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        sc.close();
        for(int i=a;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 count = 0;
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        sc.close();
        for(int i=a;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 count = 0;
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        sc.close();
        for(int i=a;i>=1;i--){
            if(a%i == 0 && b%i==0){
                count++;
            }
            if(count==k){
                System.out.println(i);
                return;
            }
        }
        
    }
    
}