#include <iostream>
#include <map>

using namespace std;

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

    string line;
    cin >> line;

    unsigned long maxLength = 0;

    map<char, int> chars;

    for (unsigned long i = 0; i < line.length(); i++) {
        for (char letter : line) {
            chars[letter]++;
        }

        if (line.length() - i <= maxLength) {
            break;
        }

        for (unsigned long j = line.length() - 1; j >= i; j--) {
            int oddAmount = 0;

            for (char letter = 'a'; letter <= 'z'; letter++) {
                if (chars[letter] % 2 != 0) {
                    oddAmount++;
                }
                if (oddAmount > 1) break;
            }

            chars[line[j]]--;

            if (oddAmount < 2 && (j - i + 1) > maxLength) {
                maxLength = j - i + 1;
                break;
            }
        }

        chars[line[i]]--;
    }

    cout << maxLength << endl;

    return 0;
}