import java.io.BufferedReader;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.StringTokenizer;
import java.util.List;
import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        InputStream in = System.in;
        OutputStream out = System.out;
        FastScanner fs = new FastScanner(in);
        PrintWriter pw = new PrintWriter(out);
        int A = fs.nextInt(), B = fs.nextInt(), K = fs.nextInt();
        List<Integer> list = new ArrayList<>();
        if(A < B) {
            B += A;
            A = B - A;
            B = B - A;
        }
        for(int i = 1; i <= A; i++) {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        }
        pw.println(list.get(list.size() - K));
        pw.close();
    }
}

class FastScanner {

    private BufferedReader reader = null;
    private StringTokenizer tokenizer = null;
 
    public FastScanner(InputStream in) {
        reader = new BufferedReader(new InputStreamReader(in));
        tokenizer = null;
    }
 
    public String next() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }
    public String nextLine() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                    throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken("\n");
    }
 
    public long nextLong() {
        return Long.parseLong(next());
    }
 
    public int nextInt() {
        return Integer.parseInt(next());
    }
 
    public double nextDouble() {
        return Double.parseDouble(next());
    }
 
    public int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = nextInt();
        return a;
    }
 
    public long[] nextLongArray(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) a[i] = nextLong();
        return a;
    }
 
} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStream; InputStream java.io import java.io.OutputStream; OutputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.IOException; IOException java.io import java.util.StringTokenizer; StringTokenizer java.util import java.util.List; List java.util import java.util.ArrayList; ArrayList java.util public class Main {
    public static void main(String[] args) {
        InputStream in = System.in;
        OutputStream out = System.out;
        FastScanner fs = new FastScanner(in);
        PrintWriter pw = new PrintWriter(out);
        int A = fs.nextInt(), B = fs.nextInt(), K = fs.nextInt();
        List<Integer> list = new ArrayList<>();
        if(A < B) {
            B += A;
            A = B - A;
            B = B - A;
        }
        for(int i = 1; i <= A; i++) {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        }
        pw.println(list.get(list.size() - K));
        pw.close();
    }
} Main public static void main(String[] args) {
        InputStream in = System.in;
        OutputStream out = System.out;
        FastScanner fs = new FastScanner(in);
        PrintWriter pw = new PrintWriter(out);
        int A = fs.nextInt(), B = fs.nextInt(), K = fs.nextInt();
        List<Integer> list = new ArrayList<>();
        if(A < B) {
            B += A;
            A = B - A;
            B = B - A;
        }
        for(int i = 1; i <= A; i++) {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        }
        pw.println(list.get(list.size() - K));
        pw.close();
    } main {
        InputStream in = System.in;
        OutputStream out = System.out;
        FastScanner fs = new FastScanner(in);
        PrintWriter pw = new PrintWriter(out);
        int A = fs.nextInt(), B = fs.nextInt(), K = fs.nextInt();
        List<Integer> list = new ArrayList<>();
        if(A < B) {
            B += A;
            A = B - A;
            B = B - A;
        }
        for(int i = 1; i <= A; i++) {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        }
        pw.println(list.get(list.size() - K));
        pw.close();
    } InputStream in = System.in; in System.in System System.in OutputStream out = System.out; out System.out System System.out FastScanner fs = new FastScanner(in); fs new FastScanner(in) PrintWriter pw = new PrintWriter(out); pw new PrintWriter(out) int A = fs.nextInt() A fs.nextInt() fs.nextInt fs B = fs.nextInt() B fs.nextInt() fs.nextInt fs K = fs.nextInt(); K fs.nextInt() fs.nextInt fs List<Integer> list = new ArrayList<>(); list new ArrayList<>() if(A < B) {
            B += A;
            A = B - A;
            B = B - A;
        } A < B A B {
            B += A;
            A = B - A;
            B = B - A;
        } B += A B A A = B - A A B - A B A B = B - A B B - A B A for(int i = 1; i <= A; i++) {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        } int i = 1; int i = 1; i 1 i <= A i A i++ i++ i {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        } {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        } if(A % i == 0 && B % i == 0) {
                list.add(i);
            } A % i == 0 && B % i == 0 A % i == 0 A % i A i 0 B % i == 0 B % i B i 0 {
                list.add(i);
            } list.add(i) list.add list i pw.println(list.get(list.size() - K)) pw.println pw list.get(list.size() - K) list.get list list.size() - K list.size() list.size list K pw.close() pw.close pw String[] args args class FastScanner {

    private BufferedReader reader = null;
    private StringTokenizer tokenizer = null;
 
    public FastScanner(InputStream in) {
        reader = new BufferedReader(new InputStreamReader(in));
        tokenizer = null;
    }
 
    public String next() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }
    public String nextLine() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                    throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken("\n");
    }
 
    public long nextLong() {
        return Long.parseLong(next());
    }
 
    public int nextInt() {
        return Integer.parseInt(next());
    }
 
    public double nextDouble() {
        return Double.parseDouble(next());
    }
 
    public int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = nextInt();
        return a;
    }
 
    public long[] nextLongArray(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) a[i] = nextLong();
        return a;
    }
 
} FastScanner private BufferedReader reader = null; reader null private StringTokenizer tokenizer = null; tokenizer null public FastScanner(InputStream in) {
        reader = new BufferedReader(new InputStreamReader(in));
        tokenizer = null;
    } FastScanner {
        reader = new BufferedReader(new InputStreamReader(in));
        tokenizer = null;
    } reader = new BufferedReader(new InputStreamReader(in)) reader new BufferedReader(new InputStreamReader(in)) tokenizer = null tokenizer null InputStream in in public String next() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    } next {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    } if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        } try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            } catch (IOException e) {
                throw new RuntimeException(e);
            } IOException e {
                throw new RuntimeException(e);
            } throw new RuntimeException(e); new RuntimeException(e) {
                tokenizer = new StringTokenizer(reader.readLine());
            } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public String nextLine() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                    throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken("\n");
    } nextLine {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                    throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken("\n");
    } if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                    throw new RuntimeException(e);
            }
        } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
            try {
                return reader.readLine();
            } catch (IOException e) {
                    throw new RuntimeException(e);
            }
        } try {
                return reader.readLine();
            } catch (IOException e) {
                    throw new RuntimeException(e);
            } catch (IOException e) {
                    throw new RuntimeException(e);
            } IOException e {
                    throw new RuntimeException(e);
            } throw new RuntimeException(e); new RuntimeException(e) {
                return reader.readLine();
            } return reader.readLine(); reader.readLine() reader.readLine reader return tokenizer.nextToken("\n"); tokenizer.nextToken("\n") tokenizer.nextToken tokenizer "\n" public long nextLong() {
        return Long.parseLong(next());
    } nextLong {
        return Long.parseLong(next());
    } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public int nextInt() {
        return Integer.parseInt(next());
    } nextInt {
        return Integer.parseInt(next());
    } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public double nextDouble() {
        return Double.parseDouble(next());
    } nextDouble {
        return Double.parseDouble(next());
    } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = nextInt();
        return a;
    } nextIntArray {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = nextInt();
        return a;
    } int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++) a[i] = nextInt(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a int n n public long[] nextLongArray(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) a[i] = nextLong();
        return a;
    } nextLongArray {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) a[i] = nextLong();
        return a;
    } long[] a = new long[n]; a new long[n] n for (int i = 0; i < n; i++) a[i] = nextLong(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextLong(); a[i] = nextLong() a[i] a i nextLong() nextLong return a; a int n n public class Main {
    public static void main(String[] args) {
        InputStream in = System.in;
        OutputStream out = System.out;
        FastScanner fs = new FastScanner(in);
        PrintWriter pw = new PrintWriter(out);
        int A = fs.nextInt(), B = fs.nextInt(), K = fs.nextInt();
        List<Integer> list = new ArrayList<>();
        if(A < B) {
            B += A;
            A = B - A;
            B = B - A;
        }
        for(int i = 1; i <= A; i++) {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        }
        pw.println(list.get(list.size() - K));
        pw.close();
    }
} public class Main {
    public static void main(String[] args) {
        InputStream in = System.in;
        OutputStream out = System.out;
        FastScanner fs = new FastScanner(in);
        PrintWriter pw = new PrintWriter(out);
        int A = fs.nextInt(), B = fs.nextInt(), K = fs.nextInt();
        List<Integer> list = new ArrayList<>();
        if(A < B) {
            B += A;
            A = B - A;
            B = B - A;
        }
        for(int i = 1; i <= A; i++) {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        }
        pw.println(list.get(list.size() - K));
        pw.close();
    }
} Main
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.StringTokenizer;
import java.util.List;
import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        InputStream in = System.in;
        OutputStream out = System.out;
        FastScanner fs = new FastScanner(in);
        PrintWriter pw = new PrintWriter(out);
        int A = fs.nextInt(), B = fs.nextInt(), K = fs.nextInt();
        List<Integer> list = new ArrayList<>();
        if(A < B) {
            B += A;
            A = B - A;
            B = B - A;
        }
        for(int i = 1; i <= A; i++) {
            if(A % i == 0 && B % i == 0) {
                list.add(i);
            }
        }
        pw.println(list.get(list.size() - K));
        pw.close();
    }
}

class FastScanner {

    private BufferedReader reader = null;
    private StringTokenizer tokenizer = null;
 
    public FastScanner(InputStream in) {
        reader = new BufferedReader(new InputStreamReader(in));
        tokenizer = null;
    }
 
    public String next() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }
    public String nextLine() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                    throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken("\n");
    }
 
    public long nextLong() {
        return Long.parseLong(next());
    }
 
    public int nextInt() {
        return Integer.parseInt(next());
    }
 
    public double nextDouble() {
        return Double.parseDouble(next());
    }
 
    public int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = nextInt();
        return a;
    }
 
    public long[] nextLongArray(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) a[i] = nextLong();
        return a;
    }
 
}
