This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#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
const int mxn = 2e5+10;
int N;
int Z[mxn];
bool check(int l,int r){
assert((r-l)%2==0);
if(l<=0||r>=N*2)return false;
assert(l<=r);
if(l%2==0)l++,r--;
if(r<=l)return true;
cout<<"? "<<(l+1)/2<<' '<<(r+1)/2<<endl;
/*
cerr<<"? "<<l<<' '<<r<<endl;
*/
int re;
cin>>re;
return re;
}
int main(){
cin>>N;
int cen = 1,rp = 2;
Z[1] = 1;
for(int i = 2;i<N*2;i++){
//cerr<<i<<":"<<cen<<','<<rp<<endl;
if(i>=rp);
else if(Z[cen*2-i]+i<rp){
Z[i] = Z[cen*2-i];
continue;
}
else if(Z[cen*2-i]+i>rp){
Z[i] = rp-i;
continue;
}
cen = i,rp = max(i+1,rp);
while(check(cen*2-rp,rp))rp++;
Z[i] = rp-i;
//cerr<<i<<"::"<<Z[i]<<endl;
}
//for(int i = 1;i<N*2;i++)cerr<<Z[i]<<' ';cerr<<endl;
int ans = 0;
for(int i = 1;i<N*2;i++){
if(i&1)ans = max(ans,(Z[i]+1)/2*2-1);
else{
ans = max(ans,Z[i]-(Z[i]&1));
}
}
cout<<"! "<<ans<<endl;
}
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