/* -*- coding: utf-8 -*-
 *
 * 253.cc: No.253 ロウソクの長さ - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MIN_X = 10;
const int MAX_X = 1000000000;
const int FX = 100;

/* typedef */

/* global variables */

/* subroutines */

int query(int x) {
  printf("? %d\n", x); flush(cout);
  int r;
  cin >> r;
  return r;
}

void finish(int x) {
  printf("! %d\n", x); flush(cout);
  exit(0);
}

/* main */

int main() {
  int minx = MIN_X, maxx = MAX_X;

  int r = query(FX);

  if (r < 0) maxx = FX - 1;
  else if (r > 0) minx = FX + 1;
  else finish(FX);

  for (int t = 1;; t++) {
    int x = (minx + maxx) / 2;
    int r = query(x - t);
    if (r < 0) maxx = x - 1;
    else if (r > 0) minx = x + 1;
    else finish(x);
  }
  return 0;
}