#include <iostream>
#include <set>

using namespace std;

int main() {
    int length;
    cin >> length;

    string line;
    cin >> line;

    unsigned long maxLength = 0;

    multiset<char> chars;

    for (unsigned long i = 0; i < line.length(); i++) {
        for (unsigned long j = i; j < line.length(); j++) {
            chars.insert(line[j]);
            int oddAmount = 0;
            for (char letter = 'a'; letter <= 'z'; letter++) {
                if (chars.count(letter) % 2 != 0) {
                    oddAmount++;
                }
                if (oddAmount > 1) break;
            }
            if (oddAmount < 2 && (j - i + 1) > maxLength) {
                maxLength = j - i + 1;
            }
        }

        chars.clear();
    }

    cout << maxLength << endl;

    return 0;
}