import java.util.*;
class Main{
    static Scanner sc=new Scanner(System.in);
    public static void main(String[] args){
        int A = sc.nextInt();
        int B = sc.nextInt();
        int ans = -1;
        for(int i=12;i<=1000;i++){
            if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            }
        }
        System.out.println(ans);
    }
} import java.util.*; util.* java class Main{
    static Scanner sc=new Scanner(System.in);
    public static void main(String[] args){
        int A = sc.nextInt();
        int B = sc.nextInt();
        int ans = -1;
        for(int i=12;i<=1000;i++){
            if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            }
        }
        System.out.println(ans);
    }
} Main static Scanner sc=new Scanner(System.in); sc new Scanner(System.in) public static void main(String[] args){
        int A = sc.nextInt();
        int B = sc.nextInt();
        int ans = -1;
        for(int i=12;i<=1000;i++){
            if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            }
        }
        System.out.println(ans);
    } main {
        int A = sc.nextInt();
        int B = sc.nextInt();
        int ans = -1;
        for(int i=12;i<=1000;i++){
            if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            }
        }
        System.out.println(ans);
    } int A = sc.nextInt(); A sc.nextInt() sc.nextInt sc int B = sc.nextInt(); B sc.nextInt() sc.nextInt sc int ans = -1; ans -1 1 for(int i=12;i<=1000;i++){
            if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            }
        } int i=12; int i=12; i 12 i<=1000 i 1000 i++ i++ i {
            if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            }
        } {
            if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            }
        } if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            } i*8/100==A&&i/10==B i*8/100==A i*8/100 i*8 i 8 100 A i/10==B i/10 i 10 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
import java.util.*;
class Main{
    static Scanner sc=new Scanner(System.in);
    public static void main(String[] args){
        int A = sc.nextInt();
        int B = sc.nextInt();
        int ans = -1;
        for(int i=12;i<=1000;i++){
            if(i*8/100==A&&i/10==B){
                ans = i;
                break;
            }
        }
        System.out.println(ans);
    }
}