fn main() {
    let n = read();
    for i in (1..n).step_by(2) {
        println!("? {} {}", i - 1, i);
        let v = read();
        if v == i - 1 || v == i {
            println!("! {}", v ^ 1);
            return;
        }
    }
    println!("! {}", n - 1);
}

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