C.cpp

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef long double ld;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define per(i,a,n) for (int i=n-1;i>=a;i--)
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define sz(x) ((int)(x).size())
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define INF 1000000000
#define MOD 1000000007

void solve() {
    int ans = -1;
    float a,b;
    cin >> a >> b;
    int x = a/0.08, y = (b + 1)/0.1;
    rep(i,x,y) {
        if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) {
            ans = i;
            break;
        }
    }
    cout << ans << "\n";
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    //freopen("input.txt", "r", stdin);
    //freopen("output.txt", "w", stdout);
    int t = 1;
    //cin >> t;
    while (t--)
        solve();
    return 0;
}