#include<bits/stdc++.h>
using namespace std;

void answer(int x) {
    cout << '!' << ' ' << x << endl;
    exit(0);
}

void solve(int l,int r,int lst)
{
    int mid,x,y;
    mid=(l+r)>>1;
    if(l==r)
    {
        answer(l);
    }
    cout<<"? "<<mid<<"\n";
    cin>>x;
    cout.flush();
    if(x==lst)
    {
        answer(mid);
    }
    cout<<"? "<<r<<"\n";
    cin>>y;
    cout.flush();
    if(y==x)
    {
        answer(r);
    }
    // cout<<x<<" "<<y<<endl;
    if(x<y)
    {
        solve(l,max(l,mid-1),y);
    }
    else
    {
        solve(min(r-1,mid+1),r-1,y);
    }
    return;
}

int main() {
    int n;
    cin >> n;
    solve(1, n, 0);
    return 0;
}