#include <iostream>
using namespace std;
int step=1<<30,n,ans,k;
int main()
{
    cin>>n;ans=n;
    for(;step;step<<=1)if(ans>step){cout<<"? "<<ans-step;cout.flush();cin>>k;ans-=k*step;}
    cout<<ans<<'\n';cout.flush();
    return 0;
}