#include <iostream>
#include <vector>
#include <set>
#include <string>
#define LL long long

#define M 2005
#define P 1000

using namespace std;

int n;
string in;

bool ispalin(const vector<int> &histog) {
    int odd = 0;
    for (int i = 0; i < 26; ++i) {
        if (histog[i] % 2)
            odd++;
    }
    if (odd <= 1) return true;
}

bool palin(int k) {
    vector<int> histog(26, 0);
    for (int i = 0; i < k; ++i) {
        histog[in[i] - 'a']++;
    }

    if (ispalin(histog)) return true;

    for (int i = k; i < n; ++i) {
        --histog[in[i - k] - 'a'];
        ++histog[in[i] - 'a'];
        if (ispalin(histog)) return true;
    }
    return false;
}

int main()
{
    cin >> n >> in;
    for (int i = n; i > 0; --i) {
        if (palin(i)) {
            cout << i << endl;
            return 0;
        }
    }
    return 0;
}