/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
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*******************************************************************************/

#include <iostream>

using namespace std;

int main()
{
    int n;
    cin>>n;
    int st=1,dr=n;
    while(st<dr)
    {
        int m=(st+dr)/2;
        cout<<"? "<<m<<endl;
        cout.flush();
        int a;
        cin>>a;
        if(a==0)
        {
            st=m+1;
        }
        else
        {
            dr=m;
        }
    }
    cout<<"! "<<st<<"\n";
    return 0;
}