#include <bits/stdc++.h>
#define GO_BEYOND ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ll long long
#define fi first
#define se second
#define pll pair<ll, ll>
#define plll pair<ll,pll>
using namespace std;
ll query(ll l, ll r){
cout << "? " << l << ' ' << r << endl;
ll ret; cin >> ret;
return ret;
}
void solve(){
ll n; cin >> n;
ll ans=0;
// case ganjil
ll lp=1, rp=3, val;
while(rp<=n){
if(lp<=0){
lp++; rp++;
}else{
val=query(lp, rp);
if(val){
ans=max(ans, rp-lp+1);
lp--; rp++;
}else{
lp++; rp++;
}
}
}
// case genap
lp=1; rp=2;
while(rp<=n){
if(lp<=0){
lp++; rp++;
}else{
val=query(lp, rp);
if(val){
ans=max(ans, rp-lp+1);
lp--; rp++;
}else{
lp++; rp++;
}
}
}
cout << "! " << ans << endl;
}
/*
g++ sigma.cpp -o a
neven
kasurrusak
*/
int main(){
GO_BEYOND;
ll t=1;
// cin >> t;
while(t--)
solve();
}
