import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        //String str = sc.next();
        double A = sc.nextDouble();
        double B = sc.nextDouble();
        double rA = 0.08;
        double rB = 0.1;
        
        for(int i=12; i<1001; i++){
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == 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);
        //String str = sc.next();
        double A = sc.nextDouble();
        double B = sc.nextDouble();
        double rA = 0.08;
        double rB = 0.1;
        
        for(int i=12; i<1001; i++){
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == B){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        //String str = sc.next();
        double A = sc.nextDouble();
        double B = sc.nextDouble();
        double rA = 0.08;
        double rB = 0.1;
        
        for(int i=12; i<1001; i++){
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == B){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    } main {
        Scanner sc = new Scanner(System.in);
        //String str = sc.next();
        double A = sc.nextDouble();
        double B = sc.nextDouble();
        double rA = 0.08;
        double rB = 0.1;
        
        for(int i=12; i<1001; i++){
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == 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 double rA = 0.08; rA 0.08 double rB = 0.1; rB 0.1 for(int i=12; i<1001; i++){
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == B){
                System.out.println(i);
                return;
            }
        } int i=12; int i=12; i 12 i<1001 i 1001 i++ i++ i {
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == B){
                System.out.println(i);
                return;
            }
        } {
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == B){
                System.out.println(i);
                return;
            }
        } if(Math.floor(i*rA) == A && Math.floor(i*rB) == B){
                System.out.println(i);
                return;
            } Math.floor(i*rA) == A && Math.floor(i*rB) == B Math.floor(i*rA) == A Math.floor(i*rA) Math.floor Math i*rA i rA A Math.floor(i*rB) == B Math.floor(i*rB) Math.floor Math i*rB i rB 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);
        //String str = sc.next();
        double A = sc.nextDouble();
        double B = sc.nextDouble();
        double rA = 0.08;
        double rB = 0.1;
        
        for(int i=12; i<1001; i++){
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == 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);
        //String str = sc.next();
        double A = sc.nextDouble();
        double B = sc.nextDouble();
        double rA = 0.08;
        double rB = 0.1;
        
        for(int i=12; i<1001; i++){
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == 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);
        //String str = sc.next();
        double A = sc.nextDouble();
        double B = sc.nextDouble();
        double rA = 0.08;
        double rB = 0.1;
        
        for(int i=12; i<1001; i++){
            if(Math.floor(i*rA) == A && Math.floor(i*rB) == B){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}