/* -*- coding: utf-8 -*-
 *
 * 2252.cc:  No.2252 Find Zero - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

int query(int i, int j) {
  printf("? %d %d\n", i, j); fflush(stdout);

  int x;
  scanf("%d", &x);
  return x;
}

/* main */

int main() {
  int n;
  scanf("%d", &n);

  for (int i = 0; i < n; i += 2) {
    int j = i + 1;
    int x = query(i, j);
    if (i == x || j == x) {
      printf("! %d\n", (x != i) ? i : j); fflush(stdout);
      return 0;
    }
  }

  printf("! %d\n", n - 1); fflush(stdout);
  return 0;
}