#nullable enable

void Q(int x) => Console.WriteLine("? " + x);
bool I() => Console.ReadLine()!.Trim() == "1";
void F(int x) => Console.WriteLine("! " + x);

var l = 0;
var r = 1000000;
Q(l);
Q(r);
var f = I();
if (f) (l, r) = (r, l);
for (var i = 3; i <= 25; i++)
{
    if (Math.Abs(l - r) <= 1) break;
    var mid = (l + r) >> 1;
    if (f)
    {
        Q(mid);
        f = I();
        if (f) (l, r) = (mid, l);
        else r = mid;
    }
    else
    {
        var mm = (mid + l) >> 1;
        Q(mm);
        I();
        if (i == 25) break;
        i++;
        Q(mid);
        f = I();
        if (f) (l, r) = (mid, mm);
        else (l, r) = (mm, mid);
    }
}
F(l);