import java.util.Scanner;

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

        long A = sc.nextInt();
        long B = sc.nextInt();

        for(int i = 10; i < 1010; i++) {
            if((int)(i * 0.08) == A && (int)(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);

        long A = sc.nextInt();
        long B = sc.nextInt();

        for(int i = 10; i < 1010; 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);

        long A = sc.nextInt();
        long B = sc.nextInt();

        for(int i = 10; i < 1010; 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);

        long A = sc.nextInt();
        long B = sc.nextInt();

        for(int i = 10; i < 1010; 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) long A = sc.nextInt(); A sc.nextInt() sc.nextInt sc long B = sc.nextInt(); B sc.nextInt() sc.nextInt sc for(int i = 10; i < 1010; i++) {
            if((int)(i * 0.08) == A && (int)(i*0.1) == B) {
                System.out.println(i);
                return;
            }
        } int i = 10; int i = 10; i 10 i < 1010 i 1010 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);

        long A = sc.nextInt();
        long B = sc.nextInt();

        for(int i = 10; i < 1010; 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);

        long A = sc.nextInt();
        long B = sc.nextInt();

        for(int i = 10; i < 1010; 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.Scanner;

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

        long A = sc.nextInt();
        long B = sc.nextInt();

        for(int i = 10; i < 1010; i++) {
            if((int)(i * 0.08) == A && (int)(i*0.1) == B) {
                System.out.println(i);
                return;
            }
        }
        System.out.println("-1");

    }

}