import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv,
    std.functional, std.math, std.numeric, std.range, std.stdio, std.string,
    std.random, std.typecons, std.container;

ulong MAX = 1_000_100, MOD = 1_000_000_007, INF = 1_000_000_000_000;
alias sread = () => readln.chomp();
alias lread(T = long) = () => readln.chomp.to!(T);
alias aryread(T = long) = () => readln.split.to!(T[]);
alias Clue = Tuple!(long, "x", long, "y", long, "h");
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);

void main()
{
    long a, b;
    scan(a, b);
    // 面倒なので総当り,最大でも消費税は100であることからxは10000以下
    foreach (i; iota(10_000))
    {
        auto s = floor((i + 1) * 0.08);
        auto t = floor((i + 1) * 0.10);
        if (s == a && t == b)
        {
            writeln(i + 1);
            return;
        }
    }
    writeln(-1);
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}
