

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

		public static void main(String[] args) throws java.lang.Exception {
		      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		      String input[] = br.readLine().split(" ");
		      int a = Integer.parseInt(input[0]);
		      int b = Integer.parseInt(input[1]);
		      int p = 0;
		      for(int i = 1; i < 1251 ; i++) {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      }
		      if(p == 0)
		    	  System.out.println("-1");
		      else
		    	  System.out.println(p);
		}
} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io public class Main {

		public static void main(String[] args) throws java.lang.Exception {
		      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		      String input[] = br.readLine().split(" ");
		      int a = Integer.parseInt(input[0]);
		      int b = Integer.parseInt(input[1]);
		      int p = 0;
		      for(int i = 1; i < 1251 ; i++) {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      }
		      if(p == 0)
		    	  System.out.println("-1");
		      else
		    	  System.out.println(p);
		}
} Main public static void main(String[] args) throws java.lang.Exception {
		      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		      String input[] = br.readLine().split(" ");
		      int a = Integer.parseInt(input[0]);
		      int b = Integer.parseInt(input[1]);
		      int p = 0;
		      for(int i = 1; i < 1251 ; i++) {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      }
		      if(p == 0)
		    	  System.out.println("-1");
		      else
		    	  System.out.println(p);
		} main {
		      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		      String input[] = br.readLine().split(" ");
		      int a = Integer.parseInt(input[0]);
		      int b = Integer.parseInt(input[1]);
		      int p = 0;
		      for(int i = 1; i < 1251 ; i++) {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      }
		      if(p == 0)
		    	  System.out.println("-1");
		      else
		    	  System.out.println(p);
		} BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) String input[] = br.readLine().split(" "); input br.readLine().split(" ") br.readLine().split br.readLine() br.readLine br " " int a = Integer.parseInt(input[0]); a Integer.parseInt(input[0]) Integer.parseInt Integer input[0] input 0 int b = Integer.parseInt(input[1]); b Integer.parseInt(input[1]) Integer.parseInt Integer input[1] input 1 int p = 0; p 0 for(int i = 1; i < 1251 ; i++) {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      } int i = 1; int i = 1; i 1 i < 1251 i 1251 i++ i++ i {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      } {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      } double tax1 = (i * 0.08); tax1 (i * 0.08) i 0.08 double tax2 = (i * 0.1); tax2 (i * 0.1) i 0.1 if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  } a == (int)tax1 && b == (int)tax2 a == (int)tax1 a (int)tax1 b == (int)tax2 b (int)tax2 {
		    		  p = i;
		    		  break;
		    	  } p = i p i break; if(p == 0)
		    	  System.out.println("-1");
		      else
		    	  System.out.println(p); p == 0 p 0 System.out.println("-1") System.out.println System.out System System.out "-1" System.out.println(p) System.out.println System.out System System.out p String[] args args public class Main {

		public static void main(String[] args) throws java.lang.Exception {
		      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		      String input[] = br.readLine().split(" ");
		      int a = Integer.parseInt(input[0]);
		      int b = Integer.parseInt(input[1]);
		      int p = 0;
		      for(int i = 1; i < 1251 ; i++) {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      }
		      if(p == 0)
		    	  System.out.println("-1");
		      else
		    	  System.out.println(p);
		}
} public class Main {

		public static void main(String[] args) throws java.lang.Exception {
		      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		      String input[] = br.readLine().split(" ");
		      int a = Integer.parseInt(input[0]);
		      int b = Integer.parseInt(input[1]);
		      int p = 0;
		      for(int i = 1; i < 1251 ; i++) {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      }
		      if(p == 0)
		    	  System.out.println("-1");
		      else
		    	  System.out.println(p);
		}
} Main


import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

		public static void main(String[] args) throws java.lang.Exception {
		      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		      String input[] = br.readLine().split(" ");
		      int a = Integer.parseInt(input[0]);
		      int b = Integer.parseInt(input[1]);
		      int p = 0;
		      for(int i = 1; i < 1251 ; i++) {
		    	  double tax1 = (i * 0.08);
		    	  double tax2 = (i * 0.1);
		    	  if(a == (int)tax1 && b == (int)tax2 ) {
		    		  p = i;
		    		  break;
		    	  }
		      }
		      if(p == 0)
		    	  System.out.println("-1");
		      else
		    	  System.out.println(p);
		}
}