import java.util.Scanner;

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

		for (int i = 1; i <= 1000; i++) {
			if (i * 8 / 100 == a && i * 10 / 100 == 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) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		sc.close();

		for (int i = 1; i <= 1000; 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) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		sc.close();

		for (int i = 1; i <= 1000; 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();
		sc.close();

		for (int i = 1; i <= 1000; 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 sc.close() sc.close sc for (int i = 1; i <= 1000; i++) {
			if (i * 8 / 100 == a && i * 10 / 100 == b) {
				System.out.println(i);
				return;
			}
		} int i = 1; int i = 1; i 1 i <= 1000 i 1000 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) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		sc.close();

		for (int i = 1; i <= 1000; 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) throws Exception {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		sc.close();

		for (int i = 1; i <= 1000; i++) {
			if (i * 8 / 100 == a && i * 10 / 100 == b) {
				System.out.println(i);
				return;
			}
		}
		System.out.println(-1);
	}
} Main
import java.util.Scanner;

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

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