import 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();
        boolean check = false;
        for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        }
        if(!check) System.out.println(-1);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String [] args){
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        boolean check = false;
        for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        }
        if(!check) System.out.println(-1);
    }
} Main public static void main(String [] args){
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        boolean check = false;
        for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        }
        if(!check) System.out.println(-1);
    } main {
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        boolean check = false;
        for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        }
        if(!check) System.out.println(-1);
    } 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 boolean check = false; check false for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        } int i=1; int i=1; i 1 i<=1009 i 1009 i++ i++ i {
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        } {
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        } if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            } Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B Math.floor(i*0.08)==A Math.floor(i*0.08) Math.floor Math i*0.08 i 0.08 A Math.floor(i*0.1)==B Math.floor(i*0.1) Math.floor Math i*0.1 i 0.1 B {
                System.out.println(i);
                check = true;
                break;
            } System.out.println(i) System.out.println System.out System System.out i check = true check true break; if(!check) System.out.println(-1); !check check 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 A = sc.nextInt();
        int B = sc.nextInt();
        boolean check = false;
        for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        }
        if(!check) System.out.println(-1);
    }
} public class Main {
    public static void main(String [] args){
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        boolean check = false;
        for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        }
        if(!check) System.out.println(-1);
    }
} Main
import 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();
        boolean check = false;
        for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        }
        if(!check) System.out.println(-1);
    }
}