#include <bits/stdc++.h>
using namespace std;

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

	string a;
	cin >> a;

	vector<int> v(26, 0);

	for (int i = 0; i < N; i++) {
		v[a[i] - 'a']++;
	}

	/*
	for (int i = 0; i < 26; i++) {
		cout << v[i] << " ";
	}
	cout << endl;
	*/

	// n cubed
	/*
	for (int i = 0; i < N; i++) {
		for (int j = i; j < N; j++) {
			for (int k = i; k < j; k++) {
				palindrom();
			}
		}
	}
	*/

	// n squared
	//
	int max_len = 0;
	for (int i = 0; i < N; i++) {
		// cout << "i: " << i << endl;
		vector<int> v(26, 0);
		int odd = 0;
		int even = 26;
		for (int j = i; j < N; j++) {

			if (i == 0) {
				//cout << "jsme tu " << endl;


				v[a[j] - 'a']++;
				if (v[a[j] - 'a'] % 2 == 0) {
					even++;
					odd--;
				} else {
					odd++;
					even--;
				}

				/*
				for (int i = 0; i < 26; i++)
					cout << v[i] << " ";
				cout << endl;
				*/

				// cout << "odd: " << odd << endl;
				// cout << "even: " << even <<  endl;

				if (odd == 1 || odd == 0) {
					int len = 0;
					for (int i = 0; i < 26; i++) {
						len += v[i];
					}
					if (len > max_len) {
						// cout << "ZMENA: " << len << endl;
						max_len = len;
					}
				}

			}
		}
		// cout << "max_len: " << max_len << endl;
	}

	cout << max_len << endl;

	/*

	int len = 0;
	int max_odd = 0;
	int max_odd_idx = 0;
	for (int i = 0; i < 26; i++) {
		if (v[i] % 2 == 0)
			len += v[i];
		if (v[i] % 2 != 0) {
			max_odd = max(max_odd, v[i]);
			max_odd_idx = i;
		}
	}

	for (int i = 0; i < 26; i++) {
		if (v[i] % 2 != 0 && i != max_odd_idx) {
			len += v[i] - 1;
		}
	}

	cout << len + max_odd << endl;
	*/



	return 0;
}