#include <iostream>

using namespace std;

int main() {
    const int CHAR_COUNT = 20;
    int inputLength = 0;
    string line;
    cin >> inputLength;
    std::getline(cin, line);
    int maxSequenceLength = 0;
    // sudy
    bool isEven[CHAR_COUNT];
    std::getline(cin, line);
    int charCount[CHAR_COUNT] = {0};
    for (char c : line) {
        charCount[c - 'a']++;
    }

    int roundCount[CHAR_COUNT];


    for (int i = 0; i < inputLength; ++i) {
        if (inputLength - i < maxSequenceLength) {
            break;
        }
        for (int j = 0; j < CHAR_COUNT; ++j) {
            isEven[j] = true;
            roundCount[j] = charCount[j];
        }
        bool ok = true;
        int oddCount = 0;
        char c;
        int len = 0;
        for (int k = i; k < inputLength; ++k) {
            c = line[k];
            roundCount[c - 'a']--;
            len++;
            isEven[c - 'a'] = !isEven[c - 'a'];
            if (isEven[c - 'a']) {
                oddCount--;
            } else {
                oddCount++;
            }
            ok = oddCount <= 1;
            if (ok) {
                maxSequenceLength = max(maxSequenceLength, len);
            } else {
                int counter = 0;
                for (int n = 0; n < CHAR_COUNT; ++n) {
                    if (!isEven[n] && roundCount == 0) {
                        counter++;
                    }
                }
                if (counter >= 2) {
                    break;
                }
            }
        }
    }

    cout << maxSequenceLength << endl;
    return 0;
}