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

int tag;

void solve(int l,int r,int lst)
{
    if(tag==1)
    {
        return;
    }
    int mid,x,y;
    mid=(l+r + 1)>>1;
    if(l==r)
    {
        tag=1;
        cout<<"! "<<r << endl;
        exit(0);
    }
    
    cout<<"? "<<mid<< endl;
    cin>>x;
    if(x==lst)
    {
        tag=1;
        cout<<"! "<<mid << endl;
        // cout.flush();
        exit(0);
    }
    
    cout<<"? "<<r<< endl;
    cin>>y;
    if(y==x)
    {
        tag=1;
        cout<<"! "<<r  << endl;
        exit(0);
    }
    if(x < y)
    {
        solve(l,mid-1,y);
    }
    else
    {
        solve(mid+1,r-1,y);
    }
    return;
}

int main()
{
    // ios::sync_with_stdio(false);
    // cin.tie(0);
    // cout.tie(0);
    
    int n;
    cin>>n;
    tag=0;
    solve(1,n,0);
    
    return 0;
}