import java.util.Scanner;

public class Main{
 public static void main(String[] args) {
   Scanner kbd =new Scanner(System.in);
   int A=kbd.nextInt();
   int B=kbd.nextInt();
   int x=-1;
   for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   }
    System.out.println(x);
 }
}
 import java.util.Scanner; Scanner java.util public class Main{
 public static void main(String[] args) {
   Scanner kbd =new Scanner(System.in);
   int A=kbd.nextInt();
   int B=kbd.nextInt();
   int x=-1;
   for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   }
    System.out.println(x);
 }
} Main public static void main(String[] args) {
   Scanner kbd =new Scanner(System.in);
   int A=kbd.nextInt();
   int B=kbd.nextInt();
   int x=-1;
   for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   }
    System.out.println(x);
 } main {
   Scanner kbd =new Scanner(System.in);
   int A=kbd.nextInt();
   int B=kbd.nextInt();
   int x=-1;
   for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   }
    System.out.println(x);
 } Scanner kbd =new Scanner(System.in); kbd new Scanner(System.in) int A=kbd.nextInt(); A kbd.nextInt() kbd.nextInt kbd int B=kbd.nextInt(); B kbd.nextInt() kbd.nextInt kbd int x=-1; x -1 1 for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   } int i=13; int i=13; i 13 i<=1010 i 1010 i++ i++ i {
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   } {
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   } double n=Math.floor(i*0.08); n Math.floor(i*0.08) Math.floor Math i*0.08 i 0.08 double m=Math.floor(i*0.1); m Math.floor(i*0.1) Math.floor Math i*0.1 i 0.1 if(A==n&&B==m){
       x=i;
       break;
     } A==n&&B==m A==n A n B==m B m {
       x=i;
       break;
     } x=i x i break; System.out.println(x) System.out.println System.out System System.out x String[] args args public class Main{
 public static void main(String[] args) {
   Scanner kbd =new Scanner(System.in);
   int A=kbd.nextInt();
   int B=kbd.nextInt();
   int x=-1;
   for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   }
    System.out.println(x);
 }
} public class Main{
 public static void main(String[] args) {
   Scanner kbd =new Scanner(System.in);
   int A=kbd.nextInt();
   int B=kbd.nextInt();
   int x=-1;
   for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   }
    System.out.println(x);
 }
} Main
import java.util.Scanner;

public class Main{
 public static void main(String[] args) {
   Scanner kbd =new Scanner(System.in);
   int A=kbd.nextInt();
   int B=kbd.nextInt();
   int x=-1;
   for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   }
    System.out.println(x);
 }
}

