// 

fn main() {
    let mut cnt = 0;
    let mut query = |x: i32| -> i32 {
        assert!(x.abs() <= 1_000_000_000);
        assert!(cnt < 25);
        cnt += 1;
        println!("? {x}");
        if cnt > 1 {
            let v = read();
            assert!(v != -1);
            v
        } else {
            0
        }
    };
    let mut l = 1;
    let mut r = 1000000;
    let mut pre = l;
    query(l);
    while l + 2 <= r {
        let m = (l + r) / 2;
        let x = 2 * m - pre;
        let res = query(x);
        if (res == 1) ^ (pre <= m) {
            r = m;
        } else {
            l = m;
        }
        pre = x;
    }
    query(l);
    let ans = if query(r) == 1 {r} else {l};
    println!("! {}", ans);
}

fn read() -> i32 {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().parse().unwrap()
}