import java.util.*;
import java.io.*;
public class Main{
  
    public static void main(String [] args){
        Scanner sc=new Scanner(System.in);
        int a=sc.nextInt();
        int b=sc.nextInt();
        boolean found=false;
        for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        }
        if(!found){
            System.out.println(-1);
        }

    }
} import java.util.*; util.* java import java.io.*; io.* 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 found=false;
        for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        }
        if(!found){
            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 found=false;
        for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        }
        if(!found){
            System.out.println(-1);
        }

    } main {
        Scanner sc=new Scanner(System.in);
        int a=sc.nextInt();
        int b=sc.nextInt();
        boolean found=false;
        for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        }
        if(!found){
            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 found=false; found false for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        } int i=1; int i=1; i 1 i<=10000 i 10000 i++ i++ i {

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        } {

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        } if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            } ((i*8)/100)==a && ((i*10)/100)==b ((i*8)/100)==a ((i*8)/100) (i*8) i 8 100 a ((i*10)/100)==b ((i*10)/100) (i*10) i 10 100 b {
                found=true;
                System.out.println(i+" ");
                break;
            } found=true found true System.out.println(i+" ") System.out.println System.out System System.out i+" " i " " break; if(!found){
            System.out.println(-1);
        } !found found {
            System.out.println(-1);
        } 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 found=false;
        for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        }
        if(!found){
            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 found=false;
        for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        }
        if(!found){
            System.out.println(-1);
        }

    }
} Main
import java.util.*;
import java.io.*;
public class Main{
  
    public static void main(String [] args){
        Scanner sc=new Scanner(System.in);
        int a=sc.nextInt();
        int b=sc.nextInt();
        boolean found=false;
        for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        }
        if(!found){
            System.out.println(-1);
        }

    }
}