import java.util.*;
 
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        
        for(int i=1; i<=1250; 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.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        
        for(int i=1; i<=1250; 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);
        
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        
        for(int i=1; i<=1250; 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);
        
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        
        for(int i=1; i<=1250; 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) double a = sc.nextDouble(); a sc.nextDouble() sc.nextDouble sc double b = sc.nextDouble(); b sc.nextDouble() sc.nextDouble sc for(int i=1; i<=1250; 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<=1250 i 1250 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" String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        
        for(int i=1; i<=1250; 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);
        
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        
        for(int i=1; i<=1250; 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.*;
 
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        
        for(int i=1; i<=1250; i++){
            if(Math.floor(i*0.08)==a && Math.floor(i*0.1)==b){
                System.out.println(i);
                return;
            }
        }

        System.out.println("-1");
   }
}
