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();

        for (int i = 0; i < 100000; i++) {
            if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println("-1");

    }

} 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();

        for (int i = 0; i < 100000; i++) {
            if ((int)(i * 0.08) == a && (int)(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();

        for (int i = 0; i < 100000; i++) {
            if ((int)(i * 0.08) == a && (int)(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();

        for (int i = 0; i < 100000; i++) {
            if ((int)(i * 0.08) == a && (int)(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 for (int i = 0; i < 100000; i++) {
            if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        } int i = 0; int i = 0; i 0 i < 100000 i 100000 i++ i++ i {
            if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        } {
            if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        } if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) {
                System.out.println(i);
                return;
            } (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 {
                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();

        for (int i = 0; i < 100000; i++) {
            if ((int)(i * 0.08) == a && (int)(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();

        for (int i = 0; i < 100000; i++) {
            if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println("-1");

    }

} 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();

        for (int i = 0; i < 100000; i++) {
            if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println("-1");

    }

}
