#include<bits/stdc++.h>
  using namespace std;
  
  #define rep(i,a,b) for(int i=(a),i##end=(b);i<=i##end;++i)
  #define per(i,a,b) for(int i=(a),i##end=(b);i>=i##end;--i)
  mt19937 Rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
  template<typename T>void chkmax(T&x,const T&y){if(x<y)x=y;}
  template<typename T>void chkmin(T&x,const T&y){if(y<x)x=y;}
  
  #define pb push_back
  #define ALL(x) (x).begin(),(x).end()
  #define mem(x) memset((x),0,sizeof(x))
  
  typedef double db;
  typedef long long ll;
  typedef vector<int>vi;
  typedef pair<int,int>pii;
  
  typedef unsigned u32;
  typedef unsigned uint;
  typedef unsigned long long u64;
  
  namespace orzjk{
    const int SZ=1e6;
    char buf[SZ],*p1=buf,*p2=buf;
    char nc(){
      return p1==p2&&(p2=(p1=buf)+fread(buf,1,SZ,stdin),p1==p2)?EOF:*p1++;
    }
    char fub[SZ],*p3=fub,*p4=fub+SZ;
    void pc(char c){
      p3==p4&&(fwrite(fub,1,SZ,stdout),p3=fub);
      *p3++=c;
    }
    void flush(){
      fwrite(fub,1,p3-fub,stdout),p3=fub;
    }
  }
  using orzjk::nc;
  using orzjk::pc;
  
  //#define nc getchar
  //#define pc putchar
  
  int read(){
    int x=0,f=1;char c=nc();
    while(c<48)c=='-'&&(f=-1),c=nc();
    while(c>47)x=x*10+(c^48),c=nc();
    return x*f;
  }
  template<class T>void write(T x){
    static char st[41];
    if(!x)return pc(48),void();
    char*p=st;
    if(x<0)x=-x,pc('-');
    for(;x;x/=10)*p++=x%10|48;
    do{
      pc(*--p);
    }while(p!=st);
  }
  
  //const int P=1e9+7;
  const int P=998244353;
  int qp(int a,int k){
    int res=1;for(;k;k>>=1,a=1ll*a*a%P)if(k&1)res=1ll*res*a%P;return res;
  }
  
  const int maxn=1e6+10;
  int n;
  int goal;
  
  int cnt;
  int ask(int v){
    printf("? %d\n",v);
    fflush(stdout);
    
//    cnt++;
    if(1){
      int x;
      scanf("%d",&x);
      return x;
    }else{
      static bool vis[maxn];
      vis[v]=1;
      int s=0;
      rep(i,1,goal-1)s+=vis[i];
      rep(i,goal+1,n)s-=vis[i];
      return abs(s);
    }
  }
  
  void ret(int x){
    if(1){
      printf("! %d\n",x);
      fflush(stdout);
    }
  //  cerr<<cnt<<endl;
    exit(0);
  }
  
  void solve(){
    cin>>n;
//    cin>>goal;
    int l=1,r=n,dt=0;
    while(1){
      int mid=(l+r)/2;
      int a=ask(mid);
      int b=ask(r);
      if(a==0){
        ret(mid);
      }
      if(b==1){
        ret(r);
      }
      if(b==0){
        l=mid+1,r-=1;
        continue;
      }
      if(b==2){
        r=mid-1;
        dt+=2;
      }
      GG:
      mid=(l+r+1)/2;
      a=ask(mid);
      b=ask(l);
      if(a==2){
        ret(mid);
      }
      if(b==3){
        ret(l);
      }
      if(b==2){
        l+=1,r=mid-1;
        goto GG;
      }
      if(b==0){
        l=mid+1;
        continue;
      }
      assert(0);
    }
  }
  
  signed main(){
  //  freopen(".in","r",stdin);
  //  freopen(".out","w",stdout);
  //  int T;cin>>T;while(T--)solve();
    solve();
    orzjk::flush();
    return 0;
  }