import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();

        int hatipa = 0;

        for (int i = 1; i <= 1250; i++) {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        }
        System.out.println("-1");
    }
} import java.util.Scanner; Scanner 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 hatipa = 0;

        for (int i = 1; i <= 1250; i++) {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        }
        System.out.println("-1");
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();

        int hatipa = 0;

        for (int i = 1; i <= 1250; i++) {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        }
        System.out.println("-1");
    } main {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();

        int hatipa = 0;

        for (int i = 1; i <= 1250; i++) {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        }
        System.out.println("-1");
    } 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 hatipa = 0; hatipa 0 for (int i = 1; i <= 1250; i++) {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        } int i = 1; int i = 1; i 1 i <= 1250 i 1250 i++ i++ i {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        } {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        } hatipa = (int) Math.floor(i * 0.08) hatipa (int) Math.floor(i * 0.08) Math.floor Math i * 0.08 i 0.08 if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            } hatipa == a hatipa a {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            } if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                } (int) Math.floor(i * 0.1) == b (int) Math.floor(i * 0.1) Math.floor Math i * 0.1 i 0.1 b {
                    System.out.println(i);
                    return;
                } System.out.println(i) System.out.println System.out System System.out i return; System.out.println("-1") System.out.println System.out System System.out "-1" 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 hatipa = 0;

        for (int i = 1; i <= 1250; i++) {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        }
        System.out.println("-1");
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();

        int hatipa = 0;

        for (int i = 1; i <= 1250; i++) {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        }
        System.out.println("-1");
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();

        int hatipa = 0;

        for (int i = 1; i <= 1250; i++) {
            hatipa = (int) Math.floor(i * 0.08);
            if (hatipa == a) {
                if ((int) Math.floor(i * 0.1) == b) {
                    System.out.println(i);
                    return;
                }
            }
        }
        System.out.println("-1");
    }
}