import java.util.*;
public class Main {
  public static void main (String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt(), B = sc.nextInt();
    int ans = -1;
    for (int i=A; i<B*100+1; i++){
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    }
    System.out.println(ans);
  }
} import java.util.*; util.* java public class Main {
  public static void main (String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt(), B = sc.nextInt();
    int ans = -1;
    for (int i=A; i<B*100+1; i++){
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    }
    System.out.println(ans);
  }
} Main public static void main (String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt(), B = sc.nextInt();
    int ans = -1;
    for (int i=A; i<B*100+1; i++){
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    }
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt(), B = sc.nextInt();
    int ans = -1;
    for (int i=A; i<B*100+1; i++){
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    }
    System.out.println(ans);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int A = sc.nextInt() A sc.nextInt() sc.nextInt sc B = sc.nextInt(); B sc.nextInt() sc.nextInt sc int ans = -1; ans -1 1 for (int i=A; i<B*100+1; i++){
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    } int i=A; int i=A; i A i<B*100+1 i B*100+1 B*100 B 100 1 i++ i++ i {
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    } {
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    } if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       } (int)(i*0.08) == A && (int)(i*0.1) == B (int)(i*0.08) == A (int)(i*0.08) i 0.08 A (int)(i*0.1) == B (int)(i*0.1) i 0.1 B {
         ans = i;
         break;
       } ans = i ans i break; System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
  public static void main (String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt(), B = sc.nextInt();
    int ans = -1;
    for (int i=A; i<B*100+1; i++){
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    }
    System.out.println(ans);
  }
} public class Main {
  public static void main (String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt(), B = sc.nextInt();
    int ans = -1;
    for (int i=A; i<B*100+1; i++){
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    }
    System.out.println(ans);
  }
} Main
import java.util.*;
public class Main {
  public static void main (String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt(), B = sc.nextInt();
    int ans = -1;
    for (int i=A; i<B*100+1; i++){
       if ((int)(i*0.08) == A && (int)(i*0.1) == B) {
         ans = i;
         break;
       }
    }
    System.out.println(ans);
  }
}