#include <bits/stdc++.h>
#define dim 100005
#define mod 1000000007
#define int long long
#define INF  2000000000
using namespace std;
ifstream fin ("x.in");
ofstream fout("x.out");

int32_t main()
{
    int st=1,x,dr,mij,last=0;
    cin>>dr;
    while (st<=dr)
    {
        mij=(st+dr)/2;
        cout<<"? "<<mij<<'\n';
        cout.flush();
        cin>>x;
        if (x==1)
        {
            st=mij+1;
            last=mij;
        }
        else
            dr=mij-1;
    }
    cout<<"! "<<last<<'\n';
}