import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);

		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		double c = a/0.08;
		double cc = (a+1)/0.08;

		
		double d = b/0.1;
		double dd = (b+1)/0.1;
		
		boolean flag = true;
		
		Outer:for(int i =(int) Math.ceil(c); i < cc; i++) {
			
			for(int j = (int)Math.ceil(d); j < dd; j++) {
				if(i == j) {
					System.out.println(i);
					flag = false;
					break Outer;
				}
				
			}
			
		}
		
		if(flag) {
			
		System.out.println("-1");
		}
		
		

	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);

		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		double c = a/0.08;
		double cc = (a+1)/0.08;

		
		double d = b/0.1;
		double dd = (b+1)/0.1;
		
		boolean flag = true;
		
		Outer:for(int i =(int) Math.ceil(c); i < cc; i++) {
			
			for(int j = (int)Math.ceil(d); j < dd; j++) {
				if(i == j) {
					System.out.println(i);
					flag = false;
					break Outer;
				}
				
			}
			
		}
		
		if(flag) {
			
		System.out.println("-1");
		}
		
		

	}

} Main public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);

		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		double c = a/0.08;
		double cc = (a+1)/0.08;

		
		double d = b/0.1;
		double dd = (b+1)/0.1;
		
		boolean flag = true;
		
		Outer:for(int i =(int) Math.ceil(c); i < cc; i++) {
			
			for(int j = (int)Math.ceil(d); j < dd; j++) {
				if(i == j) {
					System.out.println(i);
					flag = false;
					break Outer;
				}
				
			}
			
		}
		
		if(flag) {
			
		System.out.println("-1");
		}
		
		

	} main {
		Scanner stdIn = new Scanner(System.in);

		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		double c = a/0.08;
		double cc = (a+1)/0.08;

		
		double d = b/0.1;
		double dd = (b+1)/0.1;
		
		boolean flag = true;
		
		Outer:for(int i =(int) Math.ceil(c); i < cc; i++) {
			
			for(int j = (int)Math.ceil(d); j < dd; j++) {
				if(i == j) {
					System.out.println(i);
					flag = false;
					break Outer;
				}
				
			}
			
		}
		
		if(flag) {
			
		System.out.println("-1");
		}
		
		

	} Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) int a = stdIn.nextInt(); a stdIn.nextInt() stdIn.nextInt stdIn int b = stdIn.nextInt(); b stdIn.nextInt() stdIn.nextInt stdIn double c = a/0.08; c a/0.08 a 0.08 double cc = (a+1)/0.08; cc (a+1)/0.08 (a+1) a 1 0.08 double d = b/0.1; d b/0.1 b 0.1 double dd = (b+1)/0.1; dd (b+1)/0.1 (b+1) b 1 0.1 boolean flag = true; flag true if(flag) {
			
		System.out.println("-1");
		} flag {
			
		System.out.println("-1");
		} 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 stdIn = new Scanner(System.in);

		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		double c = a/0.08;
		double cc = (a+1)/0.08;

		
		double d = b/0.1;
		double dd = (b+1)/0.1;
		
		boolean flag = true;
		
		Outer:for(int i =(int) Math.ceil(c); i < cc; i++) {
			
			for(int j = (int)Math.ceil(d); j < dd; j++) {
				if(i == j) {
					System.out.println(i);
					flag = false;
					break Outer;
				}
				
			}
			
		}
		
		if(flag) {
			
		System.out.println("-1");
		}
		
		

	}

} public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);

		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		double c = a/0.08;
		double cc = (a+1)/0.08;

		
		double d = b/0.1;
		double dd = (b+1)/0.1;
		
		boolean flag = true;
		
		Outer:for(int i =(int) Math.ceil(c); i < cc; i++) {
			
			for(int j = (int)Math.ceil(d); j < dd; j++) {
				if(i == j) {
					System.out.println(i);
					flag = false;
					break Outer;
				}
				
			}
			
		}
		
		if(flag) {
			
		System.out.println("-1");
		}
		
		

	}

} Main
import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);

		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		double c = a/0.08;
		double cc = (a+1)/0.08;

		
		double d = b/0.1;
		double dd = (b+1)/0.1;
		
		boolean flag = true;
		
		Outer:for(int i =(int) Math.ceil(c); i < cc; i++) {
			
			for(int j = (int)Math.ceil(d); j < dd; j++) {
				if(i == j) {
					System.out.println(i);
					flag = false;
					break Outer;
				}
				
			}
			
		}
		
		if(flag) {
			
		System.out.println("-1");
		}
		
		

	}

}
