#include<bits/stdc++.h>
#define int long long
#define x first
#define y second
using namespace std;
const int N = 2e5+10,M = 1<<24,mod = 1e9+7,INF=1e9;
typedef pair<int,int>PII;
int query(int x)
{
    int res;
    cout<<"? "<<x<<endl;
    cin>>res;
    return res;
}
void solve()
{
    int n;
    cin>>n;
    int l=1,r=n,last=0;
    while(l<r)
    {
        int mid = l+r+1>>1;
        int t = query(mid);
        if(t==last)
        {
            cout<<"! "<<mid<<endl;
            return;
        }
        last=t;
        t = query(l);
        if(t==last)
        {
            cout<<"! "<<l<<endl;
            return;
        }
        if(t==last-1)
        {
            l++;
            r=mid-1;
        }
        else    l=mid+1;
    }
    cout<<"! "<<l<<endl;
}
signed main()
{
    int T =1;
    //cin>>T;
    while(T--)
    {
        solve();
    }
    return 0;
}