import java.util.*;
import java.io.*;
import java.math.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        HashSet<Integer> hs = new HashSet<Integer>();
        int a = sc.nextInt();
        int b = sc.nextInt();
        for(int i = 1; i <= 1250; i++){
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} import java.util.*; util.* java import java.io.*; io.* java import java.math.*; math.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        HashSet<Integer> hs = new HashSet<Integer>();
        int a = sc.nextInt();
        int b = sc.nextInt();
        for(int i = 1; i <= 1250; i++){
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        HashSet<Integer> hs = new HashSet<Integer>();
        int a = sc.nextInt();
        int b = sc.nextInt();
        for(int i = 1; i <= 1250; i++){
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    } main {
        Scanner sc = new Scanner(System.in);
        HashSet<Integer> hs = new HashSet<Integer>();
        int a = sc.nextInt();
        int b = sc.nextInt();
        for(int i = 1; i <= 1250; i++){
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) HashSet<Integer> hs = new HashSet<Integer>(); hs new HashSet<Integer>() int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc for(int i = 1; i <= 1250; i++){
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        } int i = 1; int i = 1; i 1 i <= 1250 i 1250 i++ i++ i {
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        } {
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        } int t8 = (int)Math.floor(i*0.08); t8 (int)Math.floor(i*0.08) Math.floor Math i*0.08 i 0.08 int t10 = (int)Math.floor(i*0.1); t10 (int)Math.floor(i*0.1) Math.floor Math i*0.1 i 0.1 if(a == t8 && b == t10){
                System.out.println(i);
                return;
            } a == t8 && b == t10 a == t8 a t8 b == t10 b t10 {
                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) throws Exception {
        Scanner sc = new Scanner(System.in);
        HashSet<Integer> hs = new HashSet<Integer>();
        int a = sc.nextInt();
        int b = sc.nextInt();
        for(int i = 1; i <= 1250; i++){
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        HashSet<Integer> hs = new HashSet<Integer>();
        int a = sc.nextInt();
        int b = sc.nextInt();
        for(int i = 1; i <= 1250; i++){
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} Main
import java.util.*;
import java.io.*;
import java.math.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        HashSet<Integer> hs = new HashSet<Integer>();
        int a = sc.nextInt();
        int b = sc.nextInt();
        for(int i = 1; i <= 1250; i++){
            int t8 = (int)Math.floor(i*0.08);
            int t10 = (int)Math.floor(i*0.1);
            if(a == t8 && b == t10){
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}