#include <bits/stdc++.h>
using namespace std;
#define oo 1e9
#define fi first
#define se second
#define sp(iiii) setprecision(iiii)
#define IO ios_base::sync_with_stdio(false); cin.tie(0)
#define ms(aaaa,xxxx) memset(aaaa,xxxx,sizeof(aaaa))
#define cntbit(xxxx) __builtin_popcount(xxxx)
#define getbit(xxxx,aaaa) ((xxxx>>(aaaa-1))&1)
#define _cos(xxxx) cos(xxxx*acos(-1)/180)
#define _sin(xxxx) sin(xxxx*acos(-1)/180)
#define _tan(xxxx) tan(xxxx*acos(-1)/180)
#define PE cout<<fixed
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<pair<int,int>,int> piii;
typedef pair<long long,long long> pll;
typedef pair<pair<long long,long long>,long long> plll;
const ld pi=acos(-1);
ll n,l,r,mid,x;
int main(){
IO;
cin>>n;
l=1;
r=n;
while (l<=r) {
ll mid=(r+l)/2;
cout<<"? "<<mid<<endl;
cin>>x;
if (x==0) {
cout<<"= "<<mid<<'\n';
return 0;
}
else {
if (x==-1) {
l=mid+1;
}
else {
r=mid-1;
}
}
}
}
