

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int A = scan.nextInt();
		int B = scan.nextInt();

		int anser = -1;

		for(int i = 13;i<1010;i++) {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		}

		System.out.println(anser);
	}

} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int A = scan.nextInt();
		int B = scan.nextInt();

		int anser = -1;

		for(int i = 13;i<1010;i++) {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		}

		System.out.println(anser);
	}

} Main public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int A = scan.nextInt();
		int B = scan.nextInt();

		int anser = -1;

		for(int i = 13;i<1010;i++) {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		}

		System.out.println(anser);
	} main {

		Scanner scan = new Scanner(System.in);

		int A = scan.nextInt();
		int B = scan.nextInt();

		int anser = -1;

		for(int i = 13;i<1010;i++) {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		}

		System.out.println(anser);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int A = scan.nextInt(); A scan.nextInt() scan.nextInt scan int B = scan.nextInt(); B scan.nextInt() scan.nextInt scan int anser = -1; anser -1 1 for(int i = 13;i<1010;i++) {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		} int i = 13; int i = 13; i 13 i<1010 i 1010 i++ i++ i {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		} {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		} if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			} (int)(i*0.08) == A && (int)(i*0.1) == B (int)(i*0.08) == A (int)(i*0.08) i 0.08 A (int)(i*0.1) == B (int)(i*0.1) i 0.1 B {
				anser = i;
				break;
			} anser = i anser i break; System.out.println(anser) System.out.println System.out System System.out anser String[] args args public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int A = scan.nextInt();
		int B = scan.nextInt();

		int anser = -1;

		for(int i = 13;i<1010;i++) {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		}

		System.out.println(anser);
	}

} public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int A = scan.nextInt();
		int B = scan.nextInt();

		int anser = -1;

		for(int i = 13;i<1010;i++) {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		}

		System.out.println(anser);
	}

} Main


import java.util.Scanner;

public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int A = scan.nextInt();
		int B = scan.nextInt();

		int anser = -1;

		for(int i = 13;i<1010;i++) {
			if((int)(i*0.08) == A && (int)(i*0.1) == B) {
				anser = i;
				break;
			}
		}

		System.out.println(anser);
	}

}
