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);
        CTaxIncrease solver = new CTaxIncrease();
        solver.solve(1, in, out);
        out.close();
    }

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

            int r = -1;
            for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            }
            out.append(String.valueOf(r));
        }

    }
}
 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);
        CTaxIncrease solver = new CTaxIncrease();
        solver.solve(1, in, out);
        out.close();
    }

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

            int r = -1;
            for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            }
            out.append(String.valueOf(r));
        }

    }
} 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);
        CTaxIncrease solver = new CTaxIncrease();
        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);
        CTaxIncrease solver = new CTaxIncrease();
        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) CTaxIncrease solver = new CTaxIncrease(); solver new CTaxIncrease() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class CTaxIncrease {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            int r = -1;
            for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            }
            out.append(String.valueOf(r));
        }

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

            int r = -1;
            for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            }
            out.append(String.valueOf(r));
        } solve {
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());

            int r = -1;
            for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            }
            out.append(String.valueOf(r));
        } 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 int r = -1; r -1 1 for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            } double i = 1; double i = 1; i 1 i <= 1000 i 1000 i++ i++ i {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            } {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            } boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b; result (int) (i * 0.08) == a && (int) (i * 0.1) == b (int) (i * 0.08) == a (int) (i * 0.08) i 0.08 a (int) (i * 0.1) == b (int) (i * 0.1) i 0.1 b if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                } result {
                    r = (int) i;
                    break;
                } r = (int) i r (int) i break; if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                } (int) (i * 0.08) > a || (int) (i * 0.1) > b (int) (i * 0.08) > a (int) (i * 0.08) i 0.08 a (int) (i * 0.1) > b (int) (i * 0.1) i 0.1 b {
                    break;
                } break; out.append(String.valueOf(r)) out.append out String.valueOf(r) String.valueOf String r 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);
        CTaxIncrease solver = new CTaxIncrease();
        solver.solve(1, in, out);
        out.close();
    }

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

            int r = -1;
            for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            }
            out.append(String.valueOf(r));
        }

    }
} 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);
        CTaxIncrease solver = new CTaxIncrease();
        solver.solve(1, in, out);
        out.close();
    }

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

            int r = -1;
            for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            }
            out.append(String.valueOf(r));
        }

    }
} 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);
        CTaxIncrease solver = new CTaxIncrease();
        solver.solve(1, in, out);
        out.close();
    }

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

            int r = -1;
            for (double i = 1; i <= 1000; i++) {
                boolean result = (int) (i * 0.08) == a && (int) (i * 0.1) == b;
                if (result) {
                    r = (int) i;
                    break;
                } else if ((int) (i * 0.08) > a || (int) (i * 0.1) > b) {
                    break;
                }
            }
            out.append(String.valueOf(r));
        }

    }
}

