Palindrome quiz

#include <iostream>
#include <locale>

using namespace std;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	char book[1000001];
	int i=0;
	while (cin >> book[i]) {
		++i;
	}
	int s=0;
	int e=i-1;
	while (s<e) {
		if (!isalpha(book[s])) {
			++s;
			continue;
		}
		if (!isalpha(book[e])) {
			--e;
			continue;
		}
		if (tolower(book[s]) != tolower(book[e])) {
			cout << "NO\n";
			return 0;
		}
		++s; --e;

	}
	cout << "YES\n";
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED