#include <bits/stdc++.h>
using namespace std;

int main()
{
   int n;
   cin>>n;
   int st=1,dr=n,rez=-1;
   while(st<dr)
   {
       int mij=(st+dr)/2;
       cout<<"?"<<mij<<endl;///endl face si flush-ul
       int rasp;
       cin>>rasp;
       if(rasp==0)
        st=mij+1;
       if(rasp==-1)
         return 0;
       if(rasp==1)
       {
           rez=mij;
           dr=mij;
       }
   }
   cout<<"!"<<rez<<endl;
    return 0;
}