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();

		int minPercent10 = b * 10;
		int maxPercent10 = b * 10 + 9;

		int answer = -1;
		for (int i = minPercent10; i <= maxPercent10; i++) {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		}

		System.out.println(answer);

	}
} 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();

		int minPercent10 = b * 10;
		int maxPercent10 = b * 10 + 9;

		int answer = -1;
		for (int i = minPercent10; i <= maxPercent10; i++) {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		}

		System.out.println(answer);

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

		int minPercent10 = b * 10;
		int maxPercent10 = b * 10 + 9;

		int answer = -1;
		for (int i = minPercent10; i <= maxPercent10; i++) {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		}

		System.out.println(answer);

	} main {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();

		int minPercent10 = b * 10;
		int maxPercent10 = b * 10 + 9;

		int answer = -1;
		for (int i = minPercent10; i <= maxPercent10; i++) {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		}

		System.out.println(answer);

	} 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 int minPercent10 = b * 10; minPercent10 b * 10 b 10 int maxPercent10 = b * 10 + 9; maxPercent10 b * 10 + 9 b * 10 b 10 9 int answer = -1; answer -1 1 for (int i = minPercent10; i <= maxPercent10; i++) {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		} int i = minPercent10; int i = minPercent10; i minPercent10 i <= maxPercent10 i maxPercent10 i++ i++ i {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		} {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		} if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			} (int)(0.08 * i) == a (int)(0.08 * i) 0.08 i a {
				answer = i;
				break;
			} answer = i answer i break; System.out.println(answer) System.out.println System.out System System.out answer 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();

		int minPercent10 = b * 10;
		int maxPercent10 = b * 10 + 9;

		int answer = -1;
		for (int i = minPercent10; i <= maxPercent10; i++) {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		}

		System.out.println(answer);

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

		int minPercent10 = b * 10;
		int maxPercent10 = b * 10 + 9;

		int answer = -1;
		for (int i = minPercent10; i <= maxPercent10; i++) {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		}

		System.out.println(answer);

	}
} 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();

		int minPercent10 = b * 10;
		int maxPercent10 = b * 10 + 9;

		int answer = -1;
		for (int i = minPercent10; i <= maxPercent10; i++) {
			if ((int)(0.08 * i) == a) {
				answer = i;
				break;
			}
		}

		System.out.println(answer);

	}
}