#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,popcnt,sse4")
#define pii pair<int,int>
#define fs first
#define sc second
#define ll long long
int N;
bool check(int len){
if(len<=1)return true;
for(int i = 1;i+len-1<=N;i++){
cout<<"? "<<i<<' '<<i+len-1<<endl;
int re;
cin>>re;
if(re)return true;
}
return false;
}
int main(){
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>N;
int l = 0,r = N>>1;
while(l != r){
int mid = (l+r+1)>>1;
if(check(mid*2))l = mid;
else r = mid-1;
}
int ans = l*2;
l = 1,r = (N+1)>>1;
while(l != r){
int mid = (l+r+1)>>1;
if(check(mid*2-1))l = mid;
else r = mid-1;
}
ans = max(ans,r*2-1);
cout<<"! "<<ans<<endl;
}
