#include <bits/stdc++.h>
#pragma GCC optimize(2)
using namespace std;
#define ldb long double
#define ll long long
#define ull unsigned long long
#define ill __int128
#define pb push_back
#define PII pair<ll,ll>
#define inf 0x3f3f3f3f
#define inff 0x3f3f3f3f3f3f3f3f
#define mem(a,b) memset(a,b,sizeof a)
#define yes cout<<"YES\n"
#define no cout<<"NO\n"
#define sc(a) scanf("%lf",&a);
const ll N = 1e6+10 ;
const ll mod = 1e9+7;
const ll esp=1e-6;
bool cmp(ll a,ll b){return a>b;}
ll lowbit(ll x){return x&-x;}
ll gcd(ll a,ll b){return b==0?a:gcd(b,a%b);}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
ll exgcd(ll a,ll b,ll &x,ll &y){if(!b){x=1,y=0;return a;}ll d=exgcd(b,a%b,y,x);y-=a/b*x;return d;}
ll ksm(ll a,ll b,ll c){ll sum=1;while(b){if(b&1)sum=sum*a%c;a=a*a%c;b>>=1;}return sum;}
ll addm(ll a,ll b,ll c){return (a%c+b%c)%c;}
ll faddm(ll a,ll b){return (((a%b)+b)%b);}
//inline void print(__int128 x){if(x<0){putchar('-');x=-x;}if(x>9) print(x/10);putchar(x%10+'0');}
//void read(__int128 &x){x=0;int f=1;char ch=getchar();while (!isdigit(ch)){if (ch=='-')f=-1;ch=getchar();}while(isdigit(ch)){x=x*10+ch-48;ch=getchar();}x*=f;}
//ll fact[N],infact[N];void init(ll n){fact[0]=1;for(int i=1;i<=n;i++) fact[i]=(fact[i-1]*i)%mod;infact[n]=ksm(fact[n],mod-2,mod);for(int i=n-1;i>=0;i--) infact[i]=infact[i+1]*(i+1)%mod;}ll cmb( ll a , ll b ){if(b>a) return 0 ;return (((fact[a]*infact[a-b])%mod)*infact[b])%mod ;}
//ll h[N],e[N*2],ne[N*2],w[N*2],idx;void add(ll a,ll b,ll c){e[idx]=b,ne[idx]=h[a],h[a]=idx,w[idx++]=c;}
//ll fa[N],siz[N];ll ifind(ll x){return x==fa[x]?x:fa[x]=ifind(fa[x]);}
ll ask(ll x)
{
    cout<<"? "<<x<<"\n";
    cout.flush() ;
    ll z;
    cin>>z;
    return z;
}
void solve()
{
    ll n;
    cin>>n;
    ll start=1;
    ll last=1;
    ll cnt=0;
    ll l=0,r=0;
    while(start<n)
    {
        ll u=ask(start);
        if(u>cnt)//如果我当前的值大于上一个就继续找
        {
            cnt=u;
        }
        else if(u==cnt)//如果等于那一定就这一个
        {
            cout<<"! "<<start<<"\n";
            cout.flush() ;
            return;
        }
        else//如果小于上一个的话就已经确定了
        {
            l=last+1;//上一个
            r=start-1;//这个
            cnt=u;
            break;
        }
        last=start;
        start*=2ll;
    }
    if(l==0)
    {
        l=last+1;
        r=n;
    }
    while(l<=r)
    {
        ll mid=l+r>>1;
        ll z=ask(mid);
        if(z==cnt)
        {
            cout<<"! "<<mid<<"\n";
            cout.flush() ;
            return;
        }
        else if(z<cnt)
        {
            r=mid-1;
            cnt=z;
        }
        else
        {
            l=mid+1;
            cnt=z;
        }
    }
}
int main(){
   // ios::sync_with_stdio(0); cin.tie(0);cout.tie(0);
    ll tt = 1;
   // freopen("input.txt", "r", stdin);
 //   cin >> tt ;
    while( tt-- ) solve() ;
    return 0 ;
}