import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt(), b = scanner.nextInt();
        int ans = -1;
        for (int i = 1; i <= 1000; i ++){
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        }
        System.out.println(ans);

    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt(), b = scanner.nextInt();
        int ans = -1;
        for (int i = 1; i <= 1000; i ++){
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        }
        System.out.println(ans);

    }
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt(), b = scanner.nextInt();
        int ans = -1;
        for (int i = 1; i <= 1000; i ++){
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        }
        System.out.println(ans);

    } main {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt(), b = scanner.nextInt();
        int ans = -1;
        for (int i = 1; i <= 1000; i ++){
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        }
        System.out.println(ans);

    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int a = scanner.nextInt() a scanner.nextInt() scanner.nextInt scanner b = scanner.nextInt(); b scanner.nextInt() scanner.nextInt scanner int ans = -1; ans -1 1 for (int i = 1; i <= 1000; i ++){
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        } int i = 1; int i = 1; i 1 i <= 1000 i 1000 i ++ i ++ i {
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        } {
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        } if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            } (int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b (int)Math.floor(i * 0.08) == a (int)Math.floor(i * 0.08) Math.floor Math i * 0.08 i 0.08 a (int)Math.floor(i * 0.1) == b (int)Math.floor(i * 0.1) Math.floor Math i * 0.1 i 0.1 b {
                ans = i;
                break;
            } ans = i ans i break; System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt(), b = scanner.nextInt();
        int ans = -1;
        for (int i = 1; i <= 1000; i ++){
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        }
        System.out.println(ans);

    }
} public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt(), b = scanner.nextInt();
        int ans = -1;
        for (int i = 1; i <= 1000; i ++){
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        }
        System.out.println(ans);

    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt(), b = scanner.nextInt();
        int ans = -1;
        for (int i = 1; i <= 1000; i ++){
            if ((int)Math.floor(i * 0.08) == a && (int)Math.floor(i * 0.1) == b){
                ans = i;
                break;
            }
        }
        System.out.println(ans);

    }
}
