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();
        for (int i = 1; i <= 1100; i++) {
            if (Math.floor(i * 0.08) == a && 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();
        for (int i = 1; i <= 1100; i++) {
            if (Math.floor(i * 0.08) == a && 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();
        for (int i = 1; i <= 1100; i++) {
            if (Math.floor(i * 0.08) == a && 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();
        for (int i = 1; i <= 1100; i++) {
            if (Math.floor(i * 0.08) == a && 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 for (int i = 1; i <= 1100; i++) {
            if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        } int i = 1; int i = 1; i 1 i <= 1100 i 1100 i++ i++ i {
            if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        } {
            if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        } if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                System.out.println(i);
                return;
            } Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b Math.floor(i * 0.08) == a Math.floor(i * 0.08) Math.floor Math i * 0.08 i 0.08 a Math.floor(i * 0.1) == b 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 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 = 1; i <= 1100; i++) {
            if (Math.floor(i * 0.08) == a && 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();
        for (int i = 1; i <= 1100; i++) {
            if (Math.floor(i * 0.08) == a && 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();
        for (int i = 1; i <= 1100; i++) {
            if (Math.floor(i * 0.08) == a && Math.floor(i * 0.1) == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }

}
