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();
		for(int i=1;i<=1000;i++) {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		}
			
		System.out.println(-1);
		
	}	
} 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();
		for(int i=1;i<=1000;i++) {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		}
			
		System.out.println(-1);
		
	}	
} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		int a = scan.nextInt();
		int b = scan.nextInt();
		for(int i=1;i<=1000;i++) {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		}
			
		System.out.println(-1);
		
	} main {
		Scanner scan = new Scanner(System.in);
		
		int a = scan.nextInt();
		int b = scan.nextInt();
		for(int i=1;i<=1000;i++) {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		}
			
		System.out.println(-1);
		
	} 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 for(int i=1;i<=1000;i++) {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		} int i=1; int i=1; i 1 i<=1000 i 1000 i++ i++ i {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		} {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		} double x = i*0.08; x i*0.08 i 0.08 double y = i*0.1; y i*0.1 i 0.1 int eight = (int)x; eight (int)x int ten = (int)y; ten (int)y if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			} eight==a && ten==b eight==a eight a ten==b ten b {
				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 1 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();
		for(int i=1;i<=1000;i++) {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		}
			
		System.out.println(-1);
		
	}	
} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		int a = scan.nextInt();
		int b = scan.nextInt();
		for(int i=1;i<=1000;i++) {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		}
			
		System.out.println(-1);
		
	}	
} 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();
		for(int i=1;i<=1000;i++) {
			double x = i*0.08;
			double y = i*0.1;
			int eight = (int)x;
			int ten = (int)y;
			if(eight==a && ten==b) {
				System.out.println(i);
				System.exit(0);
			}
		}
			
		System.out.println(-1);
		
	}	
}
