#pragma GCC optimize("Ofast","unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define int long long
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int N;
cin >> N;
vector<bool> tested(N+1);
auto optTest = [&](int x)->bool{
if(tested[x]){
cerr<<"CALLED DOUBLE QUERY!!!\n";
return 1;
}
tested[x]=true;
cout << "? " << x << endl;
int c;cin>>c;
return c==1;
};
int offset=0;
auto getWhichPos = [&](int x){
int center = N/2ll;
if(N&1ll)center++;
int dist = x/2ll;
int ans = -1;
if(x&1)ans = center-dist;
else ans = center+dist;
if(offset)return N-ans+1;
return ans;
};
if(N<=64){ // bruteforce
optTest(getWhichPos(1));
for(int i=2;i<=N;i++){
if(optTest(getWhichPos(i))){
cout << "= " << i-1 << endl;
return 0;
}
}
cout << "= " << N << endl;
return 0;
}
int curr = 1;
optTest(getWhichPos(curr));
bool lastInward = false;
auto test = [&](int x){
assert(curr!=x);
if(curr>x){ // inward spiral
lastInward=true;
optTest(getWhichPos(x-1));
bool ans = optTest(getWhichPos(x));
curr = x;
if(!ans){
return false;
} else {
int lastCurrPos = getWhichPos(curr);
offset^=1;
curr--;
assert(getWhichPos(curr)==lastCurrPos);
return true;
}
} else { // outward spiral
lastInward=false;
optTest(getWhichPos(x));
bool ans = optTest(getWhichPos(x-1));
curr = x-1;
if(ans){
return true;
} else {
int lastCurrPos = getWhichPos(curr);
offset^=1;
curr++;
assert(getWhichPos(curr)==lastCurrPos);
return false;
}
}
};
int ans = 0;
if(N&1)ans++;
for(int jump=(1ll<<60);jump>2;jump/=2){
if(ans+jump>N)continue;
if(!test(ans+jump))ans+=jump;
}
// emulate last 2 jumps answer
if(lastInward){
for(int i=ans+3;i>=ans+1;i--){
if(!optTest(getWhichPos(i))){
cout << "= " << i << endl;
return 0;
}
}
cout << "= " << ans << endl;
return 0;
} else {
for(int i=ans+1;i<=min(ans+3,N);i++){
if(optTest(getWhichPos(i))){
cout << "= " << i-1 << endl;
return 0;
}
}
cout << "= " << min(ans+3,N) << endl;
return 0;
}
}
