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();

    for(int i=b*10; i<(b+1)*10; i++){
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    }

    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();

    for(int i=b*10; i<(b+1)*10; i++){
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    }

    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();

    for(int i=b*10; i<(b+1)*10; i++){
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    }

    System.out.println(-1);



 } main {
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();

    for(int i=b*10; i<(b+1)*10; i++){
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    }

    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 for(int i=b*10; i<(b+1)*10; i++){
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    } int i=b*10; int i=b*10; i b*10 b 10 i<(b+1)*10 i (b+1)*10 (b+1) b 1 10 i++ i++ i {
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    } {
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    } if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      } (int)(i*0.08)==a (int)(i*0.08) i 0.08 a {
        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){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();

    for(int i=b*10; i<(b+1)*10; i++){
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    }

    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();

    for(int i=b*10; i<(b+1)*10; i++){
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    }

    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();

    for(int i=b*10; i<(b+1)*10; i++){
      if((int)(i*0.08)==a){
        System.out.println(i);
        return;
      }
    }

    System.out.println(-1);



 }
}