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 result = -1;
        for (int i = 1000; i > 0; i--) {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        }
        System.out.println(result);
    }

} 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 result = -1;
        for (int i = 1000; i > 0; i--) {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        }
        System.out.println(result);
    }

} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int result = -1;
        for (int i = 1000; i > 0; i--) {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        }
        System.out.println(result);
    } main {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int result = -1;
        for (int i = 1000; i > 0; i--) {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        }
        System.out.println(result);
    } 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 result = -1; result -1 1 for (int i = 1000; i > 0; i--) {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        } int i = 1000; int i = 1000; i 1000 i > 0 i 0 i-- i-- i {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        } {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        } double a = i * 0.08; a i * 0.08 i 0.08 double b = i * 0.1; b i * 0.1 i 0.1 if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            } Math.floor(a) == A && Math.floor(b) == B Math.floor(a) == A Math.floor(a) Math.floor Math a A Math.floor(b) == B Math.floor(b) Math.floor Math b B {
                result = i;
            } result = i result i System.out.println(result) System.out.println System.out System System.out result 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 result = -1;
        for (int i = 1000; i > 0; i--) {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        }
        System.out.println(result);
    }

} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int result = -1;
        for (int i = 1000; i > 0; i--) {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        }
        System.out.println(result);
    }

} 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 result = -1;
        for (int i = 1000; i > 0; i--) {
            double a = i * 0.08;
            double b = i * 0.1;
            if (Math.floor(a) == A && Math.floor(b) == B) {
                result = i;
            }
        }
        System.out.println(result);
    }

}
