import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int first_num = sc.nextInt();
        int second_num = sc.nextInt();
        for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(-1);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int first_num = sc.nextInt();
        int second_num = sc.nextInt();
        for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(-1);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int first_num = sc.nextInt();
        int second_num = sc.nextInt();
        for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(-1);
    } main {
        Scanner sc = new Scanner(System.in);
        int first_num = sc.nextInt();
        int second_num = sc.nextInt();
        for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(-1);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int first_num = sc.nextInt(); first_num sc.nextInt() sc.nextInt sc int second_num = sc.nextInt(); second_num sc.nextInt() sc.nextInt sc for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        } int i = 1; int i = 1; i 1 i < 2000 i 2000 i++ i++ i {
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        } {
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        } if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            } Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num Math.floor(i*0.08) == first_num Math.floor(i*0.08) Math.floor Math i*0.08 i 0.08 first_num Math.floor(i*0.1) == second_num Math.floor(i*0.1) Math.floor Math i*0.1 i 0.1 second_num {
                System.out.println(i);
                System.exit(0);
            } System.out.println(i) System.out.println System.out System System.out i System.exit(0) System.exit System 0 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);
        int first_num = sc.nextInt();
        int second_num = sc.nextInt();
        for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(-1);
    }
} public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int first_num = sc.nextInt();
        int second_num = sc.nextInt();
        for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(-1);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int first_num = sc.nextInt();
        int second_num = sc.nextInt();
        for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(-1);
    }
}