use scanner::*;
fn main() {
    let mut scanner = Scanner::default();
    let n = scanner.next::<usize>();
    for i in 0..n / 2 {
        println!("? {} {}", i * 2, i * 2 + 1);
        let response = scanner.next::<usize>();
        if response == i * 2 {
            println!("! {}", i * 2 + 1);
            return;
        } else if response == i * 2 + 1 {
            println!("! {}", i * 2);
            return;
        }
    }
    println!("! {}", n - 1);
}

#[macro_export]
macro_rules! min {
    ($a:expr $(,)*) => {{
        $a
    }};
    ($a:expr, $b:expr $(,)*) => {{
        cmp::min($a, $b)
    }};
    ($a:expr, $($rest:expr),+ $(,)*)=>{{
        cmp::min($a,min!($($rest),+))
    }}
}
#[macro_export]
macro_rules! max {
    ($a:expr $(,)*) => {{
        $a
    }};
    ($a:expr, $b:expr $(,)*) => {{
        cmp::min($a, $b)
    }};
    ($a:expr, $($rest:expr),+ $(,)*)=>{{
        cmp::min($a,min!($($rest),+))
    }}
}
#[macro_export]
macro_rules! chmin{
    ($base:expr, $($cmps:expr),+ $(,)*)=>{{
        let cmp_min = min!($($cmps),+);
        if $base > cmp_min{
            $base = cmp_min;
            true
        }else{
            false
        }
    }}
}
#[macro_export]
macro_rules! chmax{
    ($base:expr, $($cmps:expr),+ $(,)*)=>{{
        let cmp_max = max!($($cmps),+);
        if $base < cmp_min{
            $base = cmp_min;
            true
        }else{
            false
        }
    }}
}
pub mod scanner {
    use std::{io::stdin, str::FromStr};

    #[derive(Default)]
    pub struct Scanner {
        buf: Vec<String>,
    }

    impl Scanner {
        pub fn next<T: FromStr>(&mut self) -> T {
            while self.buf.is_empty() {
                let mut input = String::new();
                stdin().read_line(&mut input).ok();
                self.buf = input.trim().split_whitespace().map(String::from).collect();
            }
            let token = self.buf.pop().unwrap();
            token.parse().ok().expect("Parse Error")
        }
        pub fn next_vec<T: FromStr>(&mut self, n: usize) -> Vec<T> {
            let mut v = Vec::with_capacity(n);
            for _ in 0..n {
                v.push(self.next());
            }
            v
        }
    }
}