#pragma GCC optimize("O3")
#pragma GCC optimize("fast-math")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
#define ll long long
#define pb push_back
#define nl nullptr
#define inf 0x3f3f3f3f
#define fi first
#define se second
#define pii pair<int, int>
#define mod 666013
#define dim 100055
#define dimdoi 105



using namespace std;



//ifstream fin("aiacubiti.in");
//ofstream fout("aiacubiti.out");




int main()
{
   int n, st = 1, dr = (int)1e9, mid = 0, sol = 0, val  = 0;
     cin >> n;
     dr = n;
     while(st <= dr)
     {
         mid = (st + dr) / 2;
         cout << "? " << mid << '\n';
         cout.flush();
         cin >> val;
         if(val == 0)
             st = mid + 1;
         if(val == 1)
            dr = mid - 1;
         if(val == -1)
            return 0;

     }
     cout << "! " << mid << '\n';
     cout.flush();


    return 0;
}