import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int A = scanner.nextInt();
        int B = scanner.nextInt();

        for (int i = 1 ; i <= 1000 ; i++) {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        }

        System.out.println(-1);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int A = scanner.nextInt();
        int B = scanner.nextInt();

        for (int i = 1 ; i <= 1000 ; i++) {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        }

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

        int A = scanner.nextInt();
        int B = scanner.nextInt();

        for (int i = 1 ; i <= 1000 ; i++) {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        }

        System.out.println(-1);
    } main {
        Scanner scanner = new Scanner(System.in);

        int A = scanner.nextInt();
        int B = scanner.nextInt();

        for (int i = 1 ; i <= 1000 ; i++) {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        }

        System.out.println(-1);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int A = scanner.nextInt(); A scanner.nextInt() scanner.nextInt scanner int B = scanner.nextInt(); B scanner.nextInt() scanner.nextInt scanner for (int i = 1 ; i <= 1000 ; i++) {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        } int i = 1 ; int i = 1 ; i 1 i <= 1000 i 1000 i++ i++ i {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        } {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        } int eight = (int) (i * 0.08); eight (int) (i * 0.08) i 0.08 int ten = (int) (i * 0.1); ten (int) (i * 0.1) i 0.1 if (eight == A && ten == B) {
                System.out.println(i);
                return;
            } eight == A && ten == B eight == A eight A ten == B ten B {
                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 scanner = new Scanner(System.in);

        int A = scanner.nextInt();
        int B = scanner.nextInt();

        for (int i = 1 ; i <= 1000 ; i++) {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        }

        System.out.println(-1);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int A = scanner.nextInt();
        int B = scanner.nextInt();

        for (int i = 1 ; i <= 1000 ; i++) {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        }

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

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int A = scanner.nextInt();
        int B = scanner.nextInt();

        for (int i = 1 ; i <= 1000 ; i++) {
            int eight = (int) (i * 0.08);
            int ten = (int) (i * 0.1);
            if (eight == A && ten == B) {
                System.out.println(i);
                return;
            }
        }

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