#include <bits/stdc++.h>
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define e "\n"
#define endl "\n"
using namespace std;
#define Tp template<class T>
#define Tp2 template<class T1, class T2>
#define Tps template<class T, class... Ts>
#define Tps2 template<class T1, class T2, class... Ts>
#define ff first
#define ss second
#define rev(Aa) reverse(Aa.begin(),Aa.end())
#define all(Aa) Aa.begin(),Aa.end()
#define rall(Aa) Aa.rbegin(),Aa.rend()
#define lb lower_bound
#define ub upper_bound
#define rsz resize
#define ins insert
#define mp make_pair
#define pb emplace_back
#define pf push_front
#define popb pop_back
#define popf pop_front
#define sz(Xx) (int)(Xx).size()
#define MOD 1000000007  //1e9 + 7
#define INF 2000000000 //2e9
#define DESPACITO 1000000000000000000 //1e18
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
namespace minmax {
    Tp T max (T&& A) { return A; }
    Tp T min (T&& A) { return A; }
    Tp T max (T&& A, T&& B) { return A>B?A:B; }
    Tp T min (T&& A, T&& B) { return A<B?A:B; }
    Tps T max (T&& A, Ts&&... ts) { T B = max(ts...); return A>B?A:B; }
    Tps T min (T&& A, Ts&&... ts) { T B = min(ts...); return A<B?A:B; }
    Tps T chmax(T&& A, Ts&&... ts) { A = max(A, ts...); return A; }
    Tps T chmin(T&& A, Ts&&... ts) { A = min(A, ts...); return A; }
}
namespace input { 
    Tp void re(T&& Xx) { cin >> Xx; }
    Tp2 void re(pair<T1,T2>& Pp) { re(Pp.first); re(Pp.second); }
    Tp void re(vector<T>& Aa) { for(int i = 0; i < sz(Aa); i++) re(Aa[i]); }
    Tp2 void rea(T1&& Aa, T2 t) { for(int i = 0; i < t; i++) re(Aa[i]); }
    Tps2 void rea(T1&& Aa, T2 t, Ts&&... ts) { rea(Aa, t); rea(ts...); }
    Tp2 void rea1(T1&& Aa, T2 t) { for(int i = 1; i <= t; i++) re(Aa[i]); }
    Tps2 void rea1(T1&& Aa, T2 t, Ts&... ts) { rea1(Aa, t); rea1(ts...); }
    Tps void re(T&& t, Ts&... ts) { re(t); re(ts...); }
}
namespace output {
    void pr(int Xx) { cout << Xx; }
    // void pr(num Xx) { cout << Xx; }
    void pr(bool Xx) { cout << Xx; }
    void pr(long long Xx) { cout << Xx; }
    void pr(long long unsigned Xx) { cout << Xx; }
    void pr(double Xx) { cout << Xx; }
    void pr(char Xx) { cout << Xx; }
    void pr(const string& Xx) { cout << Xx; }
    void pr(const char* Xx) { cout << Xx; }
    void pr(const char* Xx, size_t len) { cout << string(Xx, len); }
    void ps() { cout << endl; }
    void pn() { /*do nothing*/ }
    void pw() { pr(" "); }
    void pc() { pr("]"); ps(); }
    Tp2 void pr(const pair<T1,T2>& Xx) { pr(Xx.first); pw(); pr(Xx.second);}
    Tp void pr(const T&);
    bool parse(const char* t) { if(t == e) return true; return false;}
    Tp bool parse(T&& t) { return false;}
    Tp2 bool parsepair(const pair<T1,T2>& Xx) { return true; }
    Tp bool parsepair(T&& t) { return false;}
    Tp2 void psa(T1&& Aa, T2 t) { for(int i = 0; i < t; i++) pr(Aa[i]), pw(); ps(); }
    Tp2 void pna(T1&& Aa, T2 t) { for(int i = 0; i < t; i++) pr(Aa[i]), ps(); }
    Tp2 void psa2(T1&& Aa, T2 t1, T2 t2) { for(int i = 0; i < t1; i++) {for(int j = 0; j < t2; j++) pr(Aa[i][j]), pw(); ps();} }
    Tp void pr(const T& Xx) { if(!sz(Xx)) return; bool fst = 1; bool op = 0; if (parsepair(*Xx.begin())) op = 1; for (const auto& Aa: Xx) {if(!fst) pw(); if(op) pr("{"); pr(Aa), fst = 0; if(op) pr("}"); } }
    Tps void pr(const T& t, const Ts&... ts) { pr(t); pr(ts...); }
    Tps void ps(const T& t, const Ts&... ts) { pr(t); if (sizeof...(ts)) {if (!parse(t)) pw(); } ps(ts...); }
    Tp void pn(const T& t) { for (const auto& Aa: t) ps(Aa); }
    Tps void pw(const T& t, const Ts&... ts) { pr(t); if (sizeof...(ts)) pw(); pw(ts...); }
    Tps void pc(const T& t, const Ts&... ts) { bool op = 0; if (parsepair(t)) op = 1; if(op) pr("{"); pr(t); if(op) pr("}"); if (sizeof...(ts)) pr(", "); pc(ts...); }
    namespace trace {
        #define tr(Xx...) pr("[",#Xx,"] = ["), pc(Xx);
        #define tra(Xx, y...) __f0(#Xx, Xx, y)
        #define tran(Xx, n) __fn(n, #Xx, Xx) // TO DO~ variadic multidimensional
        Tp2 void __f(const char* name, const T1& Xx, const T2& y){ pr("[",y,"] = "); ps(Xx); }
        Tps2 void __f(const char* name, const T1& Xx, const T2& y, const Ts&... rest){ const char *open = strchr(name, '['); pr("[",y,"]"); __f(open+1, Xx, rest...); }
        Tps2 void __f0(const char* name, const T1& Xx, const T2& y, const Ts&... rest){ const char *open = strchr(name, '['); pr(name, size_t(open-name)); __f(name, Xx, y, rest...); }
        Tp void __fn(int n, const char* name, const T& Xx) { for(int i = 0; i < n; i++) pr(name), __f(name, Xx[i], i); }
    }
}
using namespace minmax;
using namespace input;
using namespace output;
using namespace output::trace;
using ll = long long;
using pii = pair<int, int>;
const int N = 2e3;

int32_t main() {
    IOS;
    int i, a, b;
    re(a, b);
    for(i = 1; i < N; i++)
        if(int(0.08*i) == a and int(0.1*i) == b)
            return ps(i), 0;
    ps(-1);
    return 0;
}

Measured memory_bytes: 256