#include <bits/stdc++.h>
using namespace std;
#define int long long
#define nl endl
#define hehe ios_base::sync_with_stdio(0); cin.tie(NULL); cout.tie(NULL) ;
// const int mod = 998244353;
const int mod = 1e9+7;
const int M = 2e5+5;
int gas(int a, int b){
cout << "? " << a << ' ' << b << nl;
cout.flush();
int x;
if(!(cin >> x)) exit(0);
return x;
}
void solve(){
int n; cin >> n;
if(n == 1){
cout << "! " << 1 << nl;
return;
}
int ans = 1;
vector<int> d1(n+1,0);
int l = 1, r = 0;
for(int i = 1; i <= n; i++){
int k = 1;
if(i <= r) k = min(d1[l + r - i], (r - i + 1));
while(i - k >= 1 && i + k <= n && gas(i - k, i + k) == 1) k++;
d1[i] = k;
if(i + k - 1 > r){
l = i - k + 1;
r = i + k - 1;
}
ans = max(ans, (2 * d1[i] - 1));
}
vector<int> d2(n+1,0);
l = 1; r = 0;
for(int i = 1; i <= n; i++){
int k = 0;
if(i <= r) k = min(d2[l + r - i + 1], (r - i + 1));
while(i - k - 1 >= 1 && i + k <= n && gas(i - k - 1, i + k) == 1) k++;
d2[i] = k;
if(i + k - 1 > r){
l = i - k;
r = i + k - 1;
}
ans = max(ans, (2 * d2[i]));
}
cout << "! " << ans << nl;
}
signed main(){
hehe
// int t; cin >> t;
int t = 1;
while(t--){
solve();
}
return 0;
}
