package main

import . "fmt"

func main() {
	var n int
	Scan(&n)
	for i := 0; i < n/2; i++ {
		var x, y, z int
		x, y = i, i+n/2
		Println("?", x, y)
		Scan(&z)
		if x == z || y == z {
			Println("!", x+y-z)
			return
		}
	}
	Println("!", n-1)
}