import java.util.Scanner;

public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    int a = Integer.parseInt(sc.next());
    int b = Integer.parseInt(sc.next());
    sc.close();

    for (int i = 1; i < 2000; i++) {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    }

    System.out.println(-1);
  }
} import java.util.Scanner; Scanner java.util public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    int a = Integer.parseInt(sc.next());
    int b = Integer.parseInt(sc.next());
    sc.close();

    for (int i = 1; i < 2000; i++) {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    }

    System.out.println(-1);
  }
} Main public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    int a = Integer.parseInt(sc.next());
    int b = Integer.parseInt(sc.next());
    sc.close();

    for (int i = 1; i < 2000; i++) {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    }

    System.out.println(-1);
  } main {

    Scanner sc = new Scanner(System.in);
    int a = Integer.parseInt(sc.next());
    int b = Integer.parseInt(sc.next());
    sc.close();

    for (int i = 1; i < 2000; i++) {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    }

    System.out.println(-1);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = Integer.parseInt(sc.next()); a Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int b = Integer.parseInt(sc.next()); b Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc sc.close() sc.close sc for (int i = 1; i < 2000; i++) {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    } int i = 1; int i = 1; i 1 i < 2000 i 2000 i++ i++ i {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    } {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    } if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      } (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 {
        System.out.println(i);
        System.exit(0);
      } System.out.println(i) System.out.println System.out System System.out i System.exit(0) System.exit System 0 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 = Integer.parseInt(sc.next());
    int b = Integer.parseInt(sc.next());
    sc.close();

    for (int i = 1; i < 2000; i++) {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    }

    System.out.println(-1);
  }
} public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    int a = Integer.parseInt(sc.next());
    int b = Integer.parseInt(sc.next());
    sc.close();

    for (int i = 1; i < 2000; i++) {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    }

    System.out.println(-1);
  }
} Main
import java.util.Scanner;

public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    int a = Integer.parseInt(sc.next());
    int b = Integer.parseInt(sc.next());
    sc.close();

    for (int i = 1; i < 2000; i++) {
      if ((int) (i * 0.08) == a && (int) (i * 0.1) == b) {
        System.out.println(i);
        System.exit(0);
      }
    }

    System.out.println(-1);
  }
}