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();
    sc.close();
    int count = 0;
    int ans = 0;
    for(int i=100;count<k;i--) {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    }
    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();
    sc.close();
    int count = 0;
    int ans = 0;
    for(int i=100;count<k;i--) {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    }
    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();
    sc.close();
    int count = 0;
    int ans = 0;
    for(int i=100;count<k;i--) {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    }
    System.out.println(ans);
    
  } main {
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int k = sc.nextInt();
    sc.close();
    int count = 0;
    int ans = 0;
    for(int i=100;count<k;i--) {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    }
    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 sc.close() sc.close sc int count = 0; count 0 int ans = 0; ans 0 for(int i=100;count<k;i--) {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    } int i=100; int i=100; i 100 count<k count k i-- i-- i {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    } {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    } if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	} (a%i==0) && (b%i==0) (a%i==0) a%i a i 0 (b%i==0) b%i b i 0 {
    		ans = i;
    		count++;
    	} ans = i ans i count++ count 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();
    sc.close();
    int count = 0;
    int ans = 0;
    for(int i=100;count<k;i--) {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    }
    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();
    sc.close();
    int count = 0;
    int ans = 0;
    for(int i=100;count<k;i--) {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    }
    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();
    sc.close();
    int count = 0;
    int ans = 0;
    for(int i=100;count<k;i--) {
    	if((a%i==0) && (b%i==0)) {
    		ans = i;
    		count++;
    	}
    }
    System.out.println(ans);
    
  }
}