import 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 = 101;i>0;i--){
      if(a%i==0&&b%i==0)count++;
      if(count==k){
        System.out.println(i);
        return;
      }
    }
  }
} import java.util.*; util.* java 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 = 101;i>0;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 = 101;i>0;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 = 101;i>0;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 = 101;i>0;i--){
      if(a%i==0&&b%i==0)count++;
      if(count==k){
        System.out.println(i);
        return;
      }
    } int i = 101; int i = 101; i 101 i>0 i 0 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 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 = 101;i>0;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 = 101;i>0;i--){
      if(a%i==0&&b%i==0)count++;
      if(count==k){
        System.out.println(i);
        return;
      }
    }
  }
} Main
import 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 = 101;i>0;i--){
      if(a%i==0&&b%i==0)count++;
      if(count==k){
        System.out.println(i);
        return;
      }
    }
  }
}
