// a <= (x * 0.08) < a + 1

	// b <= (x * 0.1) < b + 1


	// la ra

	// lb rb

	// ra >= rb

	// Bismillahir Rahmanir Rahim

	#include<bits/stdc++.h>
	#include<ext/pb_ds/assoc_container.hpp>
	#include<ext/pb_ds/tree_policy.hpp>

	#define ll long long
	#define ull unsigned long long
	#define pii pair<int,int>
	#define pll pair<ll,ll>
	#define xx first
	#define yy second
	#define sci(n) scanf("%d",&n)
	#define scii(n,m) scanf("%d%d",&n,&m)
	#define sciii(n,m,w) scanf("%d%d%d",&n,&m,&w)
	#define scl(n) scanf("%lld",&n)
	#define scll(n,m) scanf("%lld%lld",&n,&m)
	#define sclll(n,m,w) scanf("%lld%lld%lld",&n,&m,&w)
	#define pf(a)   printf("%d\n",a)
	#define CASE(a) printf("Case %d: ",a)
	#define dbg(i) printf("yo %d\n", i)
	#define endl '\n'
	#define READ  freopen("input.txt","r",stdin)
	#define WRITE freopen("output.txt","w",stdout);
	#define pi acos(-1)
	#define mem(a,b) memset(a,b,sizeof(a))
	#define SQR(a) (a)*(a)
	#define all(v) v.begin(),v.end()
	#define pb push_back
	#define pri priority_queue<int>
	#define rev_pri priority_queue<int,vector<int>,greater<int> >
	#define IOS ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
	#define mod 1000000007
	#define inf INT_MAX
	#define eps 1e-9

	using namespace __gnu_pbds;
	using namespace std;

	//int dx[] = {0,1,0,-1,1,1,-1,-1};
	//int dy[] = {1,0,-1,0,1,-1,-1,1};

	//ll ncr(ll n,ll r){if(n==r)return 1;if(r==1)return n;if(dp[n][r]!=-1)return dp[n][r];return dp[n][r]=ncr(n-1,r)+ncr(n-1,r-1);}

	// bit manipulations

	//bool checkbit(int mask,int bit){return mask & (1<<bit);}
	//int setbit(int mask,int bit){ return mask  (1<<bit) ; }
	//int clearbit(int mask,int bit){return mask & ~(1<<bit);}
	//int togglebit(int mask,int bit){return mask ^ (1<<bit);}

	template <typename T> T BigMod (T b,T p,T m){if (p == 0) return 1;if (p%2 == 0){T s = BigMod(b,p/2,m);return ((s%m)*(s%m))%m;}return ((b%m)*(BigMod(b,p-1,m)%m))%m;}
	template <typename T> T ModInv (T b,T m){return BigMod(b,m-2,m);}
	template <typename T> T in(){char ch;T n = 0;bool ng = false;while (1){ch = getchar();if (ch == '-'){ng = true;ch = getchar();break;}if (ch>='0' && ch<='9')     break;}while (1){n = n*10 + (ch - '0');ch = getchar();if (ch<'0' || ch>'9')   break;}return (ng?-n:n);}
	template <typename T> T POW(T B,T P){ if(P==0) return 1; if(P&1) return B*POW(B,P-1);  else return SQR(POW(B,P/2));}
	template <typename T> T Bigmod(T b,T p,T m){ if(p==0) return 1; else if (!(p&1)) return SQR(Bigmod(b,p/2,m)) % m;else return ((b % m) * Bigmod(b,p-1,m)) % m;}
	template <typename T> T Dis(T x1,T y1,T x2, T y2){return sqrt( SQR(x1-x2) + SQR(y1-y2) );}
	template <typename T> T Angle(T x1,T y1,T x2, T y2){ return atan( double(y1-y2) / double(x1-x2));}
	template <typename T> T DIFF(T a,T b) { T d = a-b;if(d<0)return -d;else return d;}
	template <typename T> T ABS(T a) {if(a<0)return -a;else return a;}
	template <typename T> T gcd(T a,T b){if(a<0)return gcd(-a,b);if(b<0)return gcd(a,-b);return (b==0)?a:gcd(b,a%b);}
	template <typename T> T lcm(T a,T b) {if(a<0)return lcm(-a,b);if(b<0)return lcm(a,-b);return a*(b/gcd(a,b));}
	template <typename T> T euclide(T a,T b,T &x,T &y) {if(a<0){T d=euclide(-a,b,x,y);x=-x;return d;}   if(b<0){T d=euclide(a,-b,x,y);y=-y;return d;}   if(b==0){x=1;y=0;return a;}else{T d=euclide(b,a%b,x,y);T t=x;x=y;y=t-(a/b)*y;return d;}}
	template <typename T> void ia (T a[],int n){for (int i=0; i<n; i++) cin >> a[i];}
	template <typename T> void pa (T a[],int n){for (int i=0; i<n-1; i++) cout << a[i] << " ";cout << a[n-1] << endl;}
	template <typename T> ll isLeft(T a,T b,T c) { return (a.x-b.x)*(b.y-c.y)-(b.x-c.x)*(a.y-b.y);}

	template<typename T>
	using ordered_set=tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;

	///********************************MY CODE STARTS HERE********************************///


	#define mxn 100005



	int main(){
	       //IOS;



	    int  a , b;
	    cin >> a >> b;

	    
	    double la =  a / 0.08;
	    double ra = (a + 1.0) / 0.08;

	    double lb = b / 0.1;
	    double rb = (b + 1.0) / 0.1;
	    la = ceil(la);
	    lb = ceil(lb);
	    ra = ceil(ra);
	    rb = ceil(rb);

	    double s = max(la, lb);
	    double f = min(ra, rb);
	    //cout << f << endl;

	    if(f <= s) return cout << -1 << endl , 0;
	    
	    int ans = s;
	    if(floor(ans * 0.08) == a && floor(ans * 0.1) == b)
	    cout << s << endl;
	    else cout << -1 << endl;














	return 0;}


Measured memory_bytes: 256