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;
        int ans = 1;
        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.*; 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;
        int ans = 1;
        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 = sc.nextInt();
        int B = sc.nextInt();
        int K = sc.nextInt();


        int count = 0;
        int ans = 1;
        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 = sc.nextInt();
        int B = sc.nextInt();
        int K = sc.nextInt();


        int count = 0;
        int ans = 1;
        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 = 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 int ans = 1; ans 1 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 = sc.nextInt();
        int B = sc.nextInt();
        int K = sc.nextInt();


        int count = 0;
        int ans = 1;
        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 = sc.nextInt();
        int B = sc.nextInt();
        int K = sc.nextInt();


        int count = 0;
        int ans = 1;
        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.*;

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;
        int ans = 1;
        for (int i = 100; i > 0; i--) {
            if (A % i == 0 && B % i == 0) {
                count++;
                if (count == K) {
                    ans = i;
                }
            }
        }

        System.out.println(ans);
    }

}
