# include <bits/stdc++.h>
# define int long long
# define vi vector<int>
# define pb push_back
# define pii pair<int, int>
# define fi first
# define se second
using namespace std;
int n, pref[100005], suff[100005], pow_key[100005];
vi odd, even, v;
const int MOD=1e9+7;
bool ask(int l, int r) {
cout << "? " << l << " " << r << endl;
int ret; cin >> ret;
return ret;
}
char sm(char a) {return a;}
char ex(char a) {
if(a=='a') return 'b';
return 'a';
}
void hassh() {
pow_key[0]=1;
for(int i=1; i<=n; i++) {
pref[i]=pref[i-1]*3+(v[i-1]-'a'+1);
pref[i]%=MOD;
pow_key[i]=pow_key[i-1]*3;
pow_key[i]%=MOD;
}
for(int i=n; i>=1; i--) {
suff[i]=suff[i+1]*3+(v[i-1]-'a'+1);
suff[i]%=MOD;
}
}
int getpref(int l, int r) {
int dif=r-l+1;
return ((((pref[r]-pref[l-1]*pow_key[dif])%MOD)+MOD)%MOD);
}
int getsuf(int l, int r) {
int dif=r-l+1;
return ((((suff[l]-suff[r+1]*pow_key[dif])%MOD)+MOD)%MOD);
}
void solve () {
cin >> n;
for(int i=1; i<=n; i++) {
if(i%2==1) odd.pb(i);
else even.pb(i);
}
v.pb('a');
for(int i=2; i<=n; i++) {
if(ask(i-1, i)) {
v.pb(sm(v.back()));
} else {
v.pb(ex(v.back()));
}
}
hassh();
int l=0, r=odd.size()-1, ret=0;
while(l<=r) {
int mid=(l+r)/2, sz=odd[mid], ok=0;
for(int i=1; i<=(n-sz+1); i++) {
int dep=i+(sz-1)/2 - 1;
int blk=i+sz-1 - (sz-1)/2 + 1;
if(getpref(i, dep)==getsuf(blk, i+sz-1)) {
ok=1;
break;
}
}
if(ok) l=mid+1, ret=mid;
else r=mid-1;
}
int ans=odd[ret];
l=0, r=even.size()-1, ret=-1;
while(l<=r) {
int mid=(l+r)/2, sz=even[mid], ok=0;
for(int i=1; i<=(n-sz+1); i++) {
int dep=i+sz/2 - 1;
int blk=i+sz-1 - sz/2 + 1;
if(getpref(i, dep)==getsuf(blk, i+sz-1)) {
ok=1;
break;
}
}
if(ok) l=mid+1, ret=mid;
else r=mid-1;
}
if(ret!=-1) ans=max(ans, even[ret]);
cout << "! " << ans << endl;
}
signed main() {
solve();
}
