import java.util.*;
import java.util.TreeMap;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int ans = -1;
    for (int i = 1; i < 1009; i++) {
      if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
} import java.util.*; util.* java import java.util.TreeMap; TreeMap 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();
    int ans = -1;
    for (int i = 1; i < 1009; i++) {
      if (Math.floor(i * 0.08) == A && Math.floor(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();
    int B = sc.nextInt();
    int ans = -1;
    for (int i = 1; i < 1009; i++) {
      if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int ans = -1;
    for (int i = 1; i < 1009; i++) {
      if (Math.floor(i * 0.08) == A && Math.floor(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 int B = sc.nextInt(); B sc.nextInt() sc.nextInt sc int ans = -1; ans -1 1 for (int i = 1; i < 1009; i++) {
      if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
        ans = i;
        break;
      }
    } int i = 1; int i = 1; i 1 i < 1009 i 1009 i++ i++ i {
      if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
        ans = i;
        break;
      }
    } {
      if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
        ans = i;
        break;
      }
    } if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
        ans = i;
        break;
      } Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B Math.floor(i * 0.08) == A Math.floor(i * 0.08) Math.floor Math i * 0.08 i 0.08 A Math.floor(i * 0.1) == B Math.floor(i * 0.1) Math.floor Math 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();
    int B = sc.nextInt();
    int ans = -1;
    for (int i = 1; i < 1009; i++) {
      if (Math.floor(i * 0.08) == A && Math.floor(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();
    int B = sc.nextInt();
    int ans = -1;
    for (int i = 1; i < 1009; i++) {
      if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
} Main
import java.util.*;
import java.util.TreeMap;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int A = sc.nextInt();
    int B = sc.nextInt();
    int ans = -1;
    for (int i = 1; i < 1009; i++) {
      if (Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
        ans = i;
        break;
      }
    }
    System.out.println(ans);
  }
}
