#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    cin>>n;
    cout<<"? 1"<<endl;
    int x;
    cin>>x;
    if(x==0)
    {
        cout<<"! 1"<<endl;
        return 0;
    }

    int l=2,r=n;
    while(l<=r)
    {
        int mid=(l+r)/2;
        cout<<"? "<<mid<<endl;
        int cur;
        cin>>cur;
        if(cur>x)
        {
            l=mid+1;
            x=cur;
        }else if(cur<x)
        {
            r=mid-1;
            x=cur;
        }else
        {
            x=cur;
            cout<<"! "<<mid<<endl;
            break;
        }

    }
}