import java.util.Scanner;
public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int chi = 0;
        int s = -1;
        for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        }
        System.out.println(s);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int chi = 0;
        int s = -1;
        for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        }
        System.out.println(s);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int chi = 0;
        int s = -1;
        for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        }
        System.out.println(s);
    } main {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int chi = 0;
        int s = -1;
        for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        }
        System.out.println(s);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc int chi = 0; chi 0 int s = -1; s -1 1 for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        } int i = 0 ; int i = 0 ; i 0 i <= 1000 && chi == 0 i <= 1000 i 1000 chi == 0 chi 0 i++ i++ i {
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        } {
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        } int aa = (int)(i * 0.08); aa (int)(i * 0.08) i 0.08 double bb = (int)(i * 0.1); bb (int)(i * 0.1) i 0.1 if(a == aa && b == bb){
                chi = 1;
                s = i;
            } a == aa && b == bb a == aa a aa b == bb b bb {
                chi = 1;
                s = i;
            } chi = 1 chi 1 s = i s i System.out.println(s) System.out.println System.out System System.out s String[] args args public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int chi = 0;
        int s = -1;
        for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        }
        System.out.println(s);
    }
} public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int chi = 0;
        int s = -1;
        for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        }
        System.out.println(s);
    }
} Main
import java.util.Scanner;
public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int chi = 0;
        int s = -1;
        for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        }
        System.out.println(s);
    }
}