import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt();

        for (int i = 1; i <= 1009; i++) {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == 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 sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt();

        for (int i = 1; i <= 1009; i++) {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == b) {
                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(), b = sc.nextInt();

        for (int i = 1; i <= 1009; i++) {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    } main {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt();

        for (int i = 1; i <= 1009; i++) {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == b) {
                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 b = sc.nextInt(); b sc.nextInt() sc.nextInt sc for (int i = 1; i <= 1009; i++) {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == b) {
                System.out.println(i);
                return;
            }
        } int i = 1; int i = 1; i 1 i <= 1009 i 1009 i++ i++ i {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == b) {
                System.out.println(i);
                return;
            }
        } {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == b) {
                System.out.println(i);
                return;
            }
        } int x = (int) Math.floor(i * 0.08); x (int) Math.floor(i * 0.08) Math.floor Math i * 0.08 i 0.08 int y = (int) Math.floor(i * 0.1); y (int) Math.floor(i * 0.1) Math.floor Math i * 0.1 i 0.1 if (x == a && y == b) {
                System.out.println(i);
                return;
            } x == a && y == b x == a x a y == b y 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 sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt();

        for (int i = 1; i <= 1009; i++) {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == b) {
                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(), b = sc.nextInt();

        for (int i = 1; i <= 1009; i++) {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == 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 sc = new Scanner(System.in);
        int a = sc.nextInt(), b = sc.nextInt();

        for (int i = 1; i <= 1009; i++) {
            int x = (int) Math.floor(i * 0.08);
            int y = (int) Math.floor(i * 0.1);
            if (x == a && y == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}