import java.io.*;
import java.math.*;
import java.util.*;
public class Main { 

	public static void main(String[] args) {   //This is literally segment tree without updates 
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int A = I.nextInt();
		int B = I.nextInt();
		int ans = -1;
		for (int chk = 1; chk<=10000; chk++) {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		}
		O.pln(ans);
	}
	public static int Check(int L, int R, int ltr, int[][] pref, String S) {
		if (L==R) {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		}
		int mid = (L+R)/2;
		int range = R-L+1;
		range/=2; //Only ever analyze one half of current [L,R] range
		int left = pref[mid][ltr]-pref[L-1][ltr]; //All letters in left half not desired letter need to
		//be switched
		left=range-left;
		left+=Check(mid+1,R,ltr+1,pref,S); //Checking right child
		
		int right = pref[R][ltr]-pref[mid][ltr]; 
		//Number of desired letters between mid+1 and R
		right=range-right; //Have to swap bads not goods
		right+=Check(L,mid,ltr+1,pref,S); //Checking left child recursion
		return Math.min(left,right);
	}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return Math.max(a,b);
		return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());};
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
	}
} import java.io.*; io.* java import java.math.*; math.* java import java.util.*; util.* java public class Main { 

	public static void main(String[] args) {   //This is literally segment tree without updates 
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int A = I.nextInt();
		int B = I.nextInt();
		int ans = -1;
		for (int chk = 1; chk<=10000; chk++) {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		}
		O.pln(ans);
	}
	public static int Check(int L, int R, int ltr, int[][] pref, String S) {
		if (L==R) {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		}
		int mid = (L+R)/2;
		int range = R-L+1;
		range/=2; //Only ever analyze one half of current [L,R] range
		int left = pref[mid][ltr]-pref[L-1][ltr]; //All letters in left half not desired letter need to
		//be switched
		left=range-left;
		left+=Check(mid+1,R,ltr+1,pref,S); //Checking right child
		
		int right = pref[R][ltr]-pref[mid][ltr]; 
		//Number of desired letters between mid+1 and R
		right=range-right; //Have to swap bads not goods
		right+=Check(L,mid,ltr+1,pref,S); //Checking left child recursion
		return Math.min(left,right);
	}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return Math.max(a,b);
		return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());};
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
	}
} Main public static void main(String[] args) {   //This is literally segment tree without updates 
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int A = I.nextInt();
		int B = I.nextInt();
		int ans = -1;
		for (int chk = 1; chk<=10000; chk++) {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		}
		O.pln(ans);
	} main {   //This is literally segment tree without updates 
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int A = I.nextInt();
		int B = I.nextInt();
		int ans = -1;
		for (int chk = 1; chk<=10000; chk++) {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		}
		O.pln(ans);
	} FastScanner I = new FastScanner(); I new FastScanner() OutPut O = new OutPut(); O new OutPut() int A = I.nextInt(); A I.nextInt() I.nextInt I int B = I.nextInt(); B I.nextInt() I.nextInt I int ans = -1; ans -1 1 for (int chk = 1; chk<=10000; chk++) {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		} int chk = 1; int chk = 1; chk 1 chk<=10000 chk 10000 chk++ chk++ chk {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		} {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		} double pr = (double)(chk); pr (double)(chk) double a = pr*0.08; a pr*0.08 pr 0.08 double b = pr*0.1; b pr*0.1 pr 0.1 a=(int)(a) a (int)(a) b=(int)(b) b (int)(b) if (a==A&&b==B) {
				ans=chk;
				break;
			} a==A&&b==B a==A a A b==B b B {
				ans=chk;
				break;
			} ans=chk ans chk break; O.pln(ans) O.pln O ans String[] args args public static int Check(int L, int R, int ltr, int[][] pref, String S) {
		if (L==R) {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		}
		int mid = (L+R)/2;
		int range = R-L+1;
		range/=2; //Only ever analyze one half of current [L,R] range
		int left = pref[mid][ltr]-pref[L-1][ltr]; //All letters in left half not desired letter need to
		//be switched
		left=range-left;
		left+=Check(mid+1,R,ltr+1,pref,S); //Checking right child
		
		int right = pref[R][ltr]-pref[mid][ltr]; 
		//Number of desired letters between mid+1 and R
		right=range-right; //Have to swap bads not goods
		right+=Check(L,mid,ltr+1,pref,S); //Checking left child recursion
		return Math.min(left,right);
	} Check {
		if (L==R) {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		}
		int mid = (L+R)/2;
		int range = R-L+1;
		range/=2; //Only ever analyze one half of current [L,R] range
		int left = pref[mid][ltr]-pref[L-1][ltr]; //All letters in left half not desired letter need to
		//be switched
		left=range-left;
		left+=Check(mid+1,R,ltr+1,pref,S); //Checking right child
		
		int right = pref[R][ltr]-pref[mid][ltr]; 
		//Number of desired letters between mid+1 and R
		right=range-right; //Have to swap bads not goods
		right+=Check(L,mid,ltr+1,pref,S); //Checking left child recursion
		return Math.min(left,right);
	} if (L==R) {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		} L==R L R {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		} int cur = S.charAt(L-1)-'a'; cur S.charAt(L-1)-'a' S.charAt(L-1) S.charAt S L-1 L 1 'a' return cur==ltr?0:1; cur==ltr?0:1 cur==ltr cur ltr 0 1 int mid = (L+R)/2; mid (L+R)/2 (L+R) L R 2 int range = R-L+1; range R-L+1 R-L R L 1 range/=2 range 2 int left = pref[mid][ltr]-pref[L-1][ltr]; left pref[mid][ltr]-pref[L-1][ltr] pref[mid][ltr] pref[mid] pref mid ltr pref[L-1][ltr] pref[L-1] pref L-1 L 1 ltr left=range-left left range-left range left left+=Check(mid+1,R,ltr+1,pref,S) left Check(mid+1,R,ltr+1,pref,S) Check mid+1 mid 1 R ltr+1 ltr 1 pref S int right = pref[R][ltr]-pref[mid][ltr]; right pref[R][ltr]-pref[mid][ltr] pref[R][ltr] pref[R] pref R ltr pref[mid][ltr] pref[mid] pref mid ltr right=range-right right range-right range right right+=Check(L,mid,ltr+1,pref,S) right Check(L,mid,ltr+1,pref,S) Check L mid ltr+1 ltr 1 pref S return Math.min(left,right); Math.min(left,right) Math.min Math left right int L L int R R int ltr ltr int[][] pref pref String S S public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;} ceil {long ans = num/den; if (num%den!=0) 
	ans++; return ans;} long ans = num/den; ans num/den num den if (num%den!=0) 
	ans++; num%den!=0 num%den num den 0 ans++ ans return ans; ans long num num long den den public static long GCD(long a, long b) {
		if (a==0||b==0) return Math.max(a,b);
		return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b));
	} GCD {
		if (a==0||b==0) return Math.max(a,b);
		return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b));
	} if (a==0||b==0) return Math.max(a,b); a==0||b==0 a==0 a 0 b==0 b 0 return Math.max(a,b); Math.max(a,b) Math.max Math a b return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b)); GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b)) GCD Math.min(a, b) Math.min Math a b Math.max(a, b)%Math.min(a, b) Math.max(a, b) Math.max Math a b Math.min(a, b) Math.min Math a b long a a long b b public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	} FastExp {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	} long ans=1; ans 1 while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		} exp>0 exp 0 {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		} if (exp%2==1) ans*=base; exp%2==1 exp%2 exp 2 1 ans*=base ans base exp/=2 exp 2 base*=base base base base%=mod base mod ans%=mod ans mod return ans; ans long base base long exp exp long mod mod public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);} ModInv {return FastExp(num,mod-2,mod);} return FastExp(num,mod-2,mod); FastExp(num,mod-2,mod) FastExp num mod-2 mod 2 mod long num num long mod mod public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	} pop { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	} int cnt = 0; cnt 0 while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		} x>0 x 0 {
			if (x%2==1) cnt++;
			x/=2;
		} if (x%2==1) cnt++; x%2==1 x%2 x 2 1 cnt++ cnt x/=2 x 2 return cnt; cnt long x x static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());};
	} FastScanner BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) StringTokenizer st=new StringTokenizer(""); st new StringTokenizer("") String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		} next {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		} while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				} !st.hasMoreTokens() st.hasMoreTokens() st.hasMoreTokens st try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				} catch (IOException e) {
					e.printStackTrace();
				} IOException e {
					e.printStackTrace();
				} e.printStackTrace() e.printStackTrace e {
					st=new StringTokenizer(br.readLine());
				} st=new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {return Integer.parseInt(next());} nextInt {return Integer.parseInt(next());} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {return Long.parseLong(next());} nextLong {return Long.parseLong(next());} return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
	} OutPut PrintWriter w = new PrintWriter(System.out); w new PrintWriter(System.out) void pln(double x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w double x x void pln(int x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w int x x void pln(long x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w long x x void pln(String x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w String x x void pln(char x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w char x x void pln(StringBuilder x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w StringBuilder x x void pln(BigInteger x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w BigInteger x x void p(int x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w int x x void p(long x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w long x x void p(String x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w String x x void p(char x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w char x x void p(StringBuilder x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w StringBuilder x x void p(BigInteger x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w BigInteger x x void p(double x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w double x x public class Main { 

	public static void main(String[] args) {   //This is literally segment tree without updates 
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int A = I.nextInt();
		int B = I.nextInt();
		int ans = -1;
		for (int chk = 1; chk<=10000; chk++) {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		}
		O.pln(ans);
	}
	public static int Check(int L, int R, int ltr, int[][] pref, String S) {
		if (L==R) {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		}
		int mid = (L+R)/2;
		int range = R-L+1;
		range/=2; //Only ever analyze one half of current [L,R] range
		int left = pref[mid][ltr]-pref[L-1][ltr]; //All letters in left half not desired letter need to
		//be switched
		left=range-left;
		left+=Check(mid+1,R,ltr+1,pref,S); //Checking right child
		
		int right = pref[R][ltr]-pref[mid][ltr]; 
		//Number of desired letters between mid+1 and R
		right=range-right; //Have to swap bads not goods
		right+=Check(L,mid,ltr+1,pref,S); //Checking left child recursion
		return Math.min(left,right);
	}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return Math.max(a,b);
		return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());};
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
	}
} public class Main { 

	public static void main(String[] args) {   //This is literally segment tree without updates 
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int A = I.nextInt();
		int B = I.nextInt();
		int ans = -1;
		for (int chk = 1; chk<=10000; chk++) {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		}
		O.pln(ans);
	}
	public static int Check(int L, int R, int ltr, int[][] pref, String S) {
		if (L==R) {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		}
		int mid = (L+R)/2;
		int range = R-L+1;
		range/=2; //Only ever analyze one half of current [L,R] range
		int left = pref[mid][ltr]-pref[L-1][ltr]; //All letters in left half not desired letter need to
		//be switched
		left=range-left;
		left+=Check(mid+1,R,ltr+1,pref,S); //Checking right child
		
		int right = pref[R][ltr]-pref[mid][ltr]; 
		//Number of desired letters between mid+1 and R
		right=range-right; //Have to swap bads not goods
		right+=Check(L,mid,ltr+1,pref,S); //Checking left child recursion
		return Math.min(left,right);
	}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return Math.max(a,b);
		return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());};
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
	}
} Main
import java.io.*;
import java.math.*;
import java.util.*;
public class Main { 

	public static void main(String[] args) {   //This is literally segment tree without updates 
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int A = I.nextInt();
		int B = I.nextInt();
		int ans = -1;
		for (int chk = 1; chk<=10000; chk++) {
			double pr = (double)(chk);
			double a = pr*0.08;
			double b = pr*0.1;
			a=(int)(a);
			b=(int)(b);
			if (a==A&&b==B) {
				ans=chk;
				break;
			}
		}
		O.pln(ans);
	}
	public static int Check(int L, int R, int ltr, int[][] pref, String S) {
		if (L==R) {
			int cur = S.charAt(L-1)-'a';
			return cur==ltr?0:1;
		}
		int mid = (L+R)/2;
		int range = R-L+1;
		range/=2; //Only ever analyze one half of current [L,R] range
		int left = pref[mid][ltr]-pref[L-1][ltr]; //All letters in left half not desired letter need to
		//be switched
		left=range-left;
		left+=Check(mid+1,R,ltr+1,pref,S); //Checking right child
		
		int right = pref[R][ltr]-pref[mid][ltr]; 
		//Number of desired letters between mid+1 and R
		right=range-right; //Have to swap bads not goods
		right+=Check(L,mid,ltr+1,pref,S); //Checking left child recursion
		return Math.min(left,right);
	}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return Math.max(a,b);
		return GCD(Math.min(a, b),Math.max(a, b)%Math.min(a, b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());};
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
	}
}
