/* -*- coding: utf-8 -*-
 *
 * 3212.cc:  No.3212 SUPER Guess the Number - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<algorithm>

using namespace std;

/* constant */

const int MIN_A = 1;
const int MAX_A = 1000000;
const int MIN_X = -1000000000;
const int MAX_X = 1000000000;

/* typedef */

/* global variables */

/* subroutines */

int query(int a, bool rf = true) {
  printf("? %d\n", a); fflush(stdout);
  if (rf) {
    int r;
    scanf("%d", &r);
    if (r < 0) exit(0);
    return r;
  }
  return 0;
}

/* main */

int main() {
  int px = MIN_A, p = 0;
  query(px, false);

  int a0 = MIN_A, a1 = MAX_A;
  while (a0 < a1) {
    if (p == 0) { // px = left side
      int a = (a0 + a1 + 1) / 2;
      int xi = a * 2 - px;
        if (query(xi)) a0 = a; // ans-px>=xi-ans
      else a1 = a;
      px = xi, p = 1;
    }
    else { // px = right side
      int a = (a0 + a1) / 2;
      int xi = a * 2 - px;
      if (query(xi)) a1 = a;
      else a0 = a;
      px = xi, p = 0;
    }
  }

  printf("! %d\n", a0); fflush(stdout);

  for (int i = 0; i < 1e9; i++);
  return 0;
}