let [|a;b|] = stdin.ReadLine().Split() |> Array.map int
let amin = (a * 100 + 7) / 8
let amax = (a + 1) * 100 / 8
let bmin = (b * 100 + 9) / 10
let bmax = (b + 1) * 100 / 10
if amin>bmax || bmin>amax then stdout.WriteLine -1
else [amin;bmin] |> List.max |> stdout.WriteLine