use std::io::Write; macro_rules! input { (source = $s:expr, $($r:tt)*) => { let mut iter = $s.split_whitespace(); let mut next = || { iter.next().unwrap() }; input_inner!{next, $($r)*} }; ($($r:tt)*) => { let stdin = std::io::stdin(); let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock())); let mut next = move || -> String{ bytes .by_ref() .map(|r|r.unwrap() as char) .skip_while(|c|c.is_whitespace()) .take_while(|c|!c.is_whitespace()) .collect() }; input_inner!{next, $($r)*} }; } macro_rules! input_inner { ($next:expr) => {}; ($next:expr, ) => {}; ($next:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($next, $t); input_inner!{$next $($r)*} }; } macro_rules! read_value { ($next:expr, ( $($t:tt),* )) => { ( $(read_value!($next, $t)),* ) }; ($next:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($next, $t)).collect::>() }; ($next:expr, chars) => { read_value!($next, String).chars().collect::>() }; ($next:expr, usize1) => { read_value!($next, usize) - 1 }; ($next:expr, $t:ty) => { $next().parse::<$t>().expect("Parse error") }; } fn read() -> usize { let mut s = String::new(); std::io::stdin().read_line(&mut s).unwrap(); s.trim().parse().unwrap() } #[allow(non_snake_case)] fn main() { let N = read(); // input! { // N: usize, // } let mut n = N/2; let mut x: usize = 0; let mut y = N-1; while n > 0 { println!("? {} {}", x, y); std::io::stdout().flush().unwrap(); let ans = read(); if ans == x { println!("! {}", y); return; } else if ans == y { println!("! {}", x); return; } x += 1; y -= 1; n -= 1; } println!("! {}", N/2); }