import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        C solver = new C();
        solver.solve(1, in, out);
        out.close();
    }

    static class C {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            }

            out.println(-1);

        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        C solver = new C();
        solver.solve(1, in, out);
        out.close();
    }

    static class C {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            }

            out.println(-1);

        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        C solver = new C();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        C solver = new C();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) C solver = new C(); solver new C() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class C {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            }

            out.println(-1);

        }

    } C public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            }

            out.println(-1);

        } solve {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            }

            out.println(-1);

        } int a = Integer.parseInt(in.next()); a Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in int b = Integer.parseInt(in.next()); b Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            } int i = 10; int i = 10; i 10 i < 1010 i 1010 i++ i++ i {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            } {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            } if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                } Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b Math.floor(i * 0.08) == a Math.floor(i * 0.08) Math.floor Math i * 0.08 i 0.08 a Math.floor(i * 0.1) == b Math.floor(i * 0.1) Math.floor Math i * 0.1 i 0.1 b {
                    out.print(i);
                    return;
                } out.print(i) out.print out i return; out.println(-1) out.println out -1 1 int testNumber testNumber Scanner in in PrintWriter out out public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        C solver = new C();
        solver.solve(1, in, out);
        out.close();
    }

    static class C {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            }

            out.println(-1);

        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        C solver = new C();
        solver.solve(1, in, out);
        out.close();
    }

    static class C {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            }

            out.println(-1);

        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        C solver = new C();
        solver.solve(1, in, out);
        out.close();
    }

    static class C {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            for (int i = 10; i < 1010; i++) {
                if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                    out.print(i);
                    return;
                }
            }

            out.println(-1);

        }

    }
}

