#include<bits/stdc++.h>
using namespace std;
int n,cntq;
string s;
bool verif(int le, int ri)
{
for(int i=0;i<=ri-le;i++)
if(s[le+i]!=s[ri-i])
return 0;
return 1;
}
int p[100005];
bool query(int le, int ri)
{
if(le<1 || ri>n || le>ri)
return 0;
if(le==ri)
return 1;
cntq++;
//return verif(le,ri);
if(cntq>200000)
{
while(1);
}
int aux;
cout<<"? "<<le<<" "<<ri<<endl;
cin>>aux;
return aux;
}
signed main()
{
cin>>n;
/*s.resize(n+2);
for(int i=1;i<=n;i++)
{
int c = rand()%26;
s[i] = c+'a';
}*/
int mxm=1;
for(int i=1;i<n;i++)
{
p[i] = mxm/2;
while(query(i-p[i],i+1+p[i]))
p[i]++;
mxm = max(mxm, 2*p[i]);
}
for(int i=1;i<=n;i++)
{
p[i] = (mxm+1)/2;
while(query(i-p[i],i+p[i]))
p[i]++;
mxm = max(mxm, 2*p[i]-1);
}
cout<<"! "<<mxm<<endl;
// cout<<cntq<<" queries\n";
return 0;
}
/**
neven
1 2 3 4 5 6 7 8 9
l r
a b c b a
1 2 3 4 5 6 7 8 9
l r
a b c c b a
*/
