import java.util.Scanner;

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

        for (int i = 1; i <= 1000; i++) {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                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();
        int b = sc.nextInt();

        for (int i = 1; i <= 1000; i++) {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                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();
        int b = sc.nextInt();

        for (int i = 1; i <= 1000; i++) {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    } main {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();

        for (int i = 1; i <= 1000; i++) {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                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 int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc for (int i = 1; i <= 1000; i++) {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        } int i = 1; int i = 1; i 1 i <= 1000 i 1000 i++ i++ i {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        } {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        } int aa = i * 8 / 100; aa i * 8 / 100 i * 8 i 8 100 int bb = i * 10 / 100; bb i * 10 / 100 i * 10 i 10 100 if (aa > 0 && bb > 0 && a == aa && b == bb) {
                System.out.println(i);
                return;
            } aa > 0 && bb > 0 && a == aa && b == bb a == aa aa > 0 && bb > 0 && a == aa && b == bb aa > 0 aa 0 bb > 0 bb 0 a == aa a aa b == bb b bb {
                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();
        int b = sc.nextInt();

        for (int i = 1; i <= 1000; i++) {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                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();
        int b = sc.nextInt();

        for (int i = 1; i <= 1000; i++) {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                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();
        int b = sc.nextInt();

        for (int i = 1; i <= 1000; i++) {
            int aa = i * 8 / 100;
            int bb = i * 10 / 100;
            if (aa > 0 && bb > 0 && a == aa && b == bb) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}