#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#if defined(__GNUC__) || defined(__clang__)
#pragma GCC optimize("Ofast,unroll-loops,inline-functions,no-stack-protector,03")
#pragma GCC target ("sse,sse2,sse3,ssse3,sse4,popcnt,abm,avx2,mmx,fma,avx,tune=native")
#pragma clang loop vectorize(enable)
#pragma clang loop interleave(enable)
#endif
#define int long long
#define sz(x) (int)x.size()
#define F first
#define S second
#define pb push_back
#define nl '\n'
#define o_set tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef pair<int, int> pii;
void file( string s = "" )
{
if( s.empty() )
return;
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}
const int N = 2e5 + 2;
const int N1 = 1e6 + 2;
const int inf = 1e9 + 2;
const int INF = 1e18 + 2;
const int mod = 1e9 + 7;
int T = 1;
int ask( int l, int r )
{
cout <<"? " <<l <<' ' <<r <<endl;
int x;
cin >>x;
return x;
}
void solve()
{
int n;
cin >>n;
if( n == 1 )
{
cout <<1;
return;
}
if( n == 2 )
{
cout <<(ask(1, 2) ? 2 : 1);
return;
}
int ans = 0;
for( int l = 1, r = 2; r <= n; ++l, ++r )
{
int ch = 0;
while( 1 <= l && r <= n && ask(l, r) )
{
ch = 1;
ans = max(ans, r - l + 1);
--l;
++r;
}
l += ch;
r -= ch;
}
for( int l = 1, r = 3; r <= n; ++l, ++r )
{
int ch = 0;
while( 1 <= l && r <= n && ask(l, r) )
{
ans = max(ans, r - l + 1);
--l;
++r;
}
l += ch;
r -= ch;
}
cout <<ans <<endl;
}
signed main()
{
file("");
// ios_base::sync_with_stdio(false);
// cin.tie(nullptr);
// cin >>T;
while( T-- )
solve();
}
