fn main() {
    let mut cnt = 0;
    let mut query = |x: i32| -> i32 {
        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;
    query(l);
    let mut op = 0;
    while l < r {
        let res = if op == 0 {
            query(r)
        } else {
            query(l)
        };
        match (op, res) {
            (0, 0) => {
                let m = (l + r) / 2;
                r = m;
            },
            (0, 1) => {
                let m = (l + r + 1) / 2;
                l = m;
                op = 1;
            },
            (1, 0) => {
                let m = (l + r + 1) / 2;
                l = m;
            },
            (1, 1) => {
                let m = (l + r) / 2;
                r = m;
                op = 0;
            }
            _ => unreachable!(),
        };
    }
    println!("! {}", l);
}

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