import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int tax1 = sc.nextInt();
        int tax2 = sc.nextInt();
        double tmp1 = -1;
        double tmp2 = 0;
        int counter = -1;
        for(int i = 1;i < 1009;i++){
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        }
        if(counter == -1){
            System.out.println(counter);
        }
    }
} import java.util.Scanner; Scanner java.util public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int tax1 = sc.nextInt();
        int tax2 = sc.nextInt();
        double tmp1 = -1;
        double tmp2 = 0;
        int counter = -1;
        for(int i = 1;i < 1009;i++){
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        }
        if(counter == -1){
            System.out.println(counter);
        }
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int tax1 = sc.nextInt();
        int tax2 = sc.nextInt();
        double tmp1 = -1;
        double tmp2 = 0;
        int counter = -1;
        for(int i = 1;i < 1009;i++){
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        }
        if(counter == -1){
            System.out.println(counter);
        }
    } main {
        Scanner sc = new Scanner(System.in);
        int tax1 = sc.nextInt();
        int tax2 = sc.nextInt();
        double tmp1 = -1;
        double tmp2 = 0;
        int counter = -1;
        for(int i = 1;i < 1009;i++){
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        }
        if(counter == -1){
            System.out.println(counter);
        }
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int tax1 = sc.nextInt(); tax1 sc.nextInt() sc.nextInt sc int tax2 = sc.nextInt(); tax2 sc.nextInt() sc.nextInt sc double tmp1 = -1; tmp1 -1 1 double tmp2 = 0; tmp2 0 int counter = -1; counter -1 1 for(int i = 1;i < 1009;i++){
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        } int i = 1; int i = 1; i 1 i < 1009 i 1009 i++ i++ i {
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        } {
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        } tmp1 = i * 0.08 tmp1 i * 0.08 i 0.08 tmp1 = Math.floor(tmp1) tmp1 Math.floor(tmp1) Math.floor Math tmp1 tmp2 = i * 0.1 tmp2 i * 0.1 i 0.1 tmp2 = Math.floor(tmp2) tmp2 Math.floor(tmp2) Math.floor Math tmp2 if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            } tmp1 == tax1 && tmp2 == tax2 tmp1 == tax1 tmp1 tax1 tmp2 == tax2 tmp2 tax2 {
                System.out.println(i);
                counter++;
                break;
            } System.out.println(i) System.out.println System.out System System.out i counter++ counter break; if(counter == -1){
            System.out.println(counter);
        } counter == -1 counter -1 1 {
            System.out.println(counter);
        } System.out.println(counter) System.out.println System.out System System.out counter String[] args args public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int tax1 = sc.nextInt();
        int tax2 = sc.nextInt();
        double tmp1 = -1;
        double tmp2 = 0;
        int counter = -1;
        for(int i = 1;i < 1009;i++){
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        }
        if(counter == -1){
            System.out.println(counter);
        }
    }
} public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int tax1 = sc.nextInt();
        int tax2 = sc.nextInt();
        double tmp1 = -1;
        double tmp2 = 0;
        int counter = -1;
        for(int i = 1;i < 1009;i++){
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        }
        if(counter == -1){
            System.out.println(counter);
        }
    }
} Main
import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int tax1 = sc.nextInt();
        int tax2 = sc.nextInt();
        double tmp1 = -1;
        double tmp2 = 0;
        int counter = -1;
        for(int i = 1;i < 1009;i++){
            tmp1 = i * 0.08;
            tmp1 = Math.floor(tmp1);
            //System.out.println(tmp1);
            tmp2 = i * 0.1;
            tmp2 = Math.floor(tmp2);
            if(tmp1 == tax1 && tmp2 == tax2){
                System.out.println(i);
                counter++;
                break;
            }
        }
        if(counter == -1){
            System.out.println(counter);
        }
    }
}