#include<bits/stdc++.h>
using namespace std;
#define x first
#define y second
typedef long long LL;
const int N=1e3+10,M=510;
int n,m;
pair<int,int>a[N],b[N];
bool flag;
int x;
int query(int x){
    int cur;
    cout<<"? "<<x<<endl;
    cout.flush();
    cin>>cur;
    return cur;
}

int main() {
    scanf("%d",&n);
    int l=1,r=n;
    int pe=0;
    while(l<=r){
        if(pe==0){
            int cur=query(l);
            if(cur==pe){
                cout<<"! "<<l<<endl;cout.flush();break;
            }
            l++;
            pe=cur;
        }
        int mid=l+r>>1;
        int cur=query(mid);
        if(cur==pe-1){
            r=mid-1;
        }else if(cur==pe){
            cout<<"! "<<l<<endl;
            cout.flush();
            break;
        }else {
            l=mid+1;
        }
        pe=cur;
    }


}