
import 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 = 0; i < 1100; i++) {
            if (i * 8 / 100 == a && i * 10 / 100 == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} import java.util.*; util.* java 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 = 0; i < 1100; i++) {
            if (i * 8 / 100 == a && i * 10 / 100 == 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();
        int b = sc.nextInt();
        for (int i = 0; i < 1100; i++) {
            if (i * 8 / 100 == a && i * 10 / 100 == b) {
                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 = 0; i < 1100; i++) {
            if (i * 8 / 100 == a && i * 10 / 100 == 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 int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc for (int i = 0; i < 1100; i++) {
            if (i * 8 / 100 == a && i * 10 / 100 == b) {
                System.out.println(i);
                return;
            }
        } int i = 0; int i = 0; i 0 i < 1100 i 1100 i++ i++ i {
            if (i * 8 / 100 == a && i * 10 / 100 == b) {
                System.out.println(i);
                return;
            }
        } {
            if (i * 8 / 100 == a && i * 10 / 100 == b) {
                System.out.println(i);
                return;
            }
        } if (i * 8 / 100 == a && i * 10 / 100 == b) {
                System.out.println(i);
                return;
            } i * 8 / 100 == a && i * 10 / 100 == b i * 8 / 100 == a i * 8 / 100 i * 8 i 8 100 a i * 10 / 100 == b i * 10 / 100 i * 10 i 10 100 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();
        int b = sc.nextInt();
        for (int i = 0; i < 1100; i++) {
            if (i * 8 / 100 == a && i * 10 / 100 == 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();
        int b = sc.nextInt();
        for (int i = 0; i < 1100; i++) {
            if (i * 8 / 100 == a && i * 10 / 100 == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
} Main

import 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 = 0; i < 1100; i++) {
            if (i * 8 / 100 == a && i * 10 / 100 == b) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}