use std::io::Write;

fn query(x: usize, y: usize) -> usize {
    println!("? {} {}", x, y);
    std::io::stdout().flush().unwrap();
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).ok();
    let mut input = input.split_whitespace();
    input.next().unwrap().parse().unwrap()
}

fn main() {
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).ok();
    let mut input = input.split_whitespace();
    let n: usize = input.next().unwrap().parse().unwrap();
    for i in 0..(n / 2) {
        let x = i * 2;
        let y = x + 1;
        let z = query(x, y);
        if z == x {
            println!("! {}", y);
            return;
        } else if z == y {
            println!("! {}", x);
            return;
        }
    }
    println!("! {}", n - 1);
}