// Slower C++ solution:
#include <bits/stdc++.h>

#define endl '\n'

#define int long long

#define lint long long

#define pii pair<int, int>

#define FOR(i, a, b) for(int i = (a); i < (b); ++i)

#define FORR(i, a, b) for(int i = (a); i > (b); --i)

#define REP(i, n) FOR(i, 0, n)

#define SZ(v) ((int)v.size())

#define ZERO(a) memset(a, 0, sizeof(a))

#define MINUS(a) memset(a, 0xff, sizeof(a))

#define FILLINF(a) memset(a, 0x3f, sizeof(a))

#define POW(n) (1LL << (n))

#define POPCNT(n) (__builtin_popcount(n))

#define IN(i, a, b) ((a) <= (i) && (i) <= (b))

using namespace std;

template <typename T> inline bool CHMIN(T& a, T b) { if(a > b) { a = b; return 1; } return 0; }

template <typename T> inline bool CHMAX(T& a, T b) { if(a < b) { a = b; return 1; } return 0; }

template <typename T> inline void SORT(T& a) { sort(begin(a), end(a)); }

template <typename T> inline void REV(T& a) { reverse(begin(a), end(a)); }

template <typename T> inline void UNI(T& a) { sort(a.begin(), a.end()); a.erase(unique(a.begin(), a.end()), a.end()); }

template <typename S, typename T> inline T LB(S& v, T a) { return *lower_bound(begin(v), end(v), a); }

template <typename S, typename T> inline int LBP(S& v, T a) { return lower_bound(begin(v), end(v), a) - begin(v); }

template <typename S, typename T> inline T UB(S& v, T a) { return *upper_bound(begin(v), end(v), a); }

template <typename S, typename T> inline int UBP(S& v, T a) { return upper_bound(begin(v), end(v), a) - begin(v); }

template <typename S, typename T> ostream& operator << (ostream& os, const pair<S, T>& p) { os << p.first << " " << p.second; return os; }

template <typename S, typename T> istream& operator >> (istream& is, pair<S, T>& p) { is >> p.first >> p.second; return is; }

template <typename T> ostream& operator << (ostream& os, const vector<T>& v) { for (int i = 0; i < v.size(); ++i) { if (i) os << " "; os << v[i]; } return os; }

template <typename T> istream& operator >> (istream& is, vector<T>& v) { for(T& in : v) is >> in; return is; }

template <typename T = int> vector<T> make_v(size_t a) { return vector<T>(a); }

template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...)); }

template <typename T, typename V> typename enable_if<is_class<T>::value == 0>::type fill_v(T& t, const V& v) { t = v; }

template <typename T, typename V> typename enable_if<is_class<T>::value != 0>::type fill_v(T& t, const V& v) { for(auto &e : t) fill_v(e, v); }

const double PI = 3.14159265358979323846;

const double EPS = 1e-10;

const lint INF = 0x3f3f3f3f3f3f3f3f;

const lint MOD = 1000000007;



void _main() {

    int A, B;

    cin >> A >> B;

    REP (i, 1000000) {

        int p8 = i * 8 / 100;

        int p10 = i / 10;

        if (p8 == A && p10 == B) {

            cout << i << endl;

            return;

        }

    }

    cout << -1 << endl;

}



signed main(signed argc, char **argv) {

    if (argc > 1) {

        if (strchr(argv[1], 'i')) freopen("input.txt", "r", stdin);

        if (strchr(argv[1], 'o')) freopen("output.txt", "w", stdout);

    }

    ios::sync_with_stdio(false);

    cin.tie(nullptr);

    cout << fixed << setprecision(10);

    _main();

    return 0;

}

// Faster C++ solution for the same problem (measured speedup: 2.700506981684033x):
#include <bits/stdc++.h>

#define int long long

#define endl '\n'

#define FOR(i, a, n) for (int i = (a); i < (n); ++i)

#define REP(i, n) FOR(i, 0, n)

using namespace std;



void _main() {

    int A, B;

    cin >> A >> B;

    for (int i = 1; i < 20000; ++i) {

        if (i * 8 / 100 == A && i / 10 == B) {

            cout << i << endl;

            return;

        }

    }

    cout << -1 << endl;

}



signed main() {

    ios::sync_with_stdio(false);

    cin.tie(nullptr);

    cout << fixed << setprecision(10);

    _main();

    return 0;

}