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 = 0;i < 10000;i++) {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				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 = 0;i < 10000;i++) {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				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 < 10000;i++) {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				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 < 10000;i++) {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				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 < 10000;i++) {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				System.out.println(i);
				return;
			}
		} int i = 0; int i = 0; i 0 i < 10000 i 10000 i++ i++ i {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				System.out.println(i);
				return;
			}
		} {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				System.out.println(i);
				return;
			}
		} double xa = (double)i * 0.08; xa (double)i * 0.08 (double)i 0.08 double xb = (double)i * 0.1; xb (double)i * 0.1 (double)i 0.1 if(a == (int)xa && b == (int)xb) {
				System.out.println(i);
				return;
			} a == (int)xa && b == (int)xb a == (int)xa a (int)xa b == (int)xb b (int)xb {
				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 < 10000;i++) {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				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 < 10000;i++) {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				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 = 0;i < 10000;i++) {
			double xa = (double)i * 0.08;
			double xb = (double)i * 0.1;
			if(a == (int)xa && b == (int)xb) {
				System.out.println(i);
				return;
			}
		}

		System.out.println(-1);
	}
}
