#include <iostream>

using namespace std;

int main()
{
    int n;
    cin>>n;
    int l=1,r=n;
    while(l<r)
    {
        int mid=(l+r)/2;
        cout<<"? "<<mid;

        int16_t rasp;
        cin>>rasp;
        if(rasp==0)
            l=mid+1;
        else
            r=mid;
    }
    cout<<"! "<<l;
    return 0;
}