import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double tax_8 = sc.nextDouble();
		double tax_10 = sc.nextDouble();
		for(int i = 0; i <= 1250; i++) {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		}
		System.out.println("-1");
	}
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double tax_8 = sc.nextDouble();
		double tax_10 = sc.nextDouble();
		for(int i = 0; i <= 1250; i++) {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		}
		System.out.println("-1");
	}
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double tax_8 = sc.nextDouble();
		double tax_10 = sc.nextDouble();
		for(int i = 0; i <= 1250; i++) {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		}
		System.out.println("-1");
	} main {
        Scanner sc = new Scanner(System.in);
        double tax_8 = sc.nextDouble();
		double tax_10 = sc.nextDouble();
		for(int i = 0; i <= 1250; i++) {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		}
		System.out.println("-1");
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double tax_8 = sc.nextDouble(); tax_8 sc.nextDouble() sc.nextDouble sc double tax_10 = sc.nextDouble(); tax_10 sc.nextDouble() sc.nextDouble sc for(int i = 0; i <= 1250; i++) {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		} int i = 0; int i = 0; i 0 i <= 1250 i 1250 i++ i++ i {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		} {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		} if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			} (int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10 (int)(i * 0.08) == tax_8 (int)(i * 0.08) i 0.08 tax_8 (int)(i * 0.1) == tax_10 (int)(i * 0.1) i 0.1 tax_10 {
				System.out.println(i);
				System.exit(0);
			} System.out.println(i) System.out.println System.out System System.out i System.exit(0) System.exit System 0 System.out.println("-1") System.out.println System.out System System.out "-1" String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double tax_8 = sc.nextDouble();
		double tax_10 = sc.nextDouble();
		for(int i = 0; i <= 1250; i++) {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		}
		System.out.println("-1");
	}
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double tax_8 = sc.nextDouble();
		double tax_10 = sc.nextDouble();
		for(int i = 0; i <= 1250; i++) {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		}
		System.out.println("-1");
	}
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double tax_8 = sc.nextDouble();
		double tax_10 = sc.nextDouble();
		for(int i = 0; i <= 1250; i++) {
			if((int)(i * 0.08) == tax_8 && (int)(i * 0.1) == tax_10) {
				System.out.println(i);
				System.exit(0);
			}
		}
		System.out.println("-1");
	}
}