#include <iostream>
#include <vector>
using namespace std;
#define ll long long
ll longestPalindrome(string s) {
string T = "#";
for (char c : s) {
T += c;
T += "#";
}
int n = T.size();
vector<int> P(n, 0);
int C = 0, R = 0; // center and right boundary
int maxLen = 0, centerIndex = 0;
for (int i = 0; i < n; i++) {
int mirror = 2*C - i;
if (i < R)
P[i] = min(R - i, P[mirror]);
// expand
while (i - P[i] - 1 >= 0 &&
i + P[i] + 1 < n &&
T[i - P[i] - 1] == T[i + P[i] + 1])
{
P[i]++;
}
// update center and right boundary
if (i + P[i] > R) {
C = i;
R = i + P[i];
}
// track max
if (P[i] > maxLen) {
maxLen = P[i];
centerIndex = i;
}
}
return maxLen;
}
int main(){
ll n;
cin >> n;
//since only a and b we just compare letter by letter
bool letters[n];
letters[0] = 1;
for (ll i = 1; i < n; ++i){
cout << "? " << i << " " << i+1 << "\n";
cout.flush();
bool same;
cin >> same;
letters[i] = same ? letters[i-1] : !letters[i-1];
}
string rec;
for (ll i = 0; i < n; ++i){
if (letters[i]) rec.push_back('a');
else rec.push_back('b');
}
cout << "! " << longestPalindrome(rec) << "\n";
cout.flush();
return 0;
}
