#include <iostream>

using namespace std;

int main() {
    int n, st, dr, mijl, rez, x;
    cin>>n;
    st = 0;
    dr = n;
    while( dr - st >= 0 ) {
      mijl = ( st + dr ) / 2;
      cout<<"? "<<mijl<<'\n';
      cout.flush();
      cin>>rez;
      if( rez == 0 )
        st = mijl + 1;
      else {
        dr = mijl - 1;
        x = mijl;
      }
    }
    cout<<"! "<<x<<'\n';
    return 0;
}