#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>
#include <array>
#include <cstdio>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

int ask(int Y){cout << "? " << Y << endl;int res;cin >> res;return res;}

int res = 1e9+1;

int solve(int curr, int depth = 0) {
  if(depth == 100) { return depth; }
  switch(ask(res)) {
    case -1:
      res -= curr;
      res --;
      break;
    case 1:
      res += curr;
      res --;
      break;
    case 0:
      return depth;
  }
  return solve(curr/2, depth+1);
}

int main(){

  {
    auto j = ask(50);
    if(j == 0) { cout << "! 50\n"; return 0; }
    else if(j == -1) {
      auto depth = solve((res = 24) / 2);
      cout << "! " << res + depth + 1 << endl;
      return 0;
    }
  }

  auto depth = solve((res = 1e9)/2, 1);
  cout << "! " << res + depth << endl;
  return 0;
}