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

static const int N = 3e5 + 10;
static const int K = 20;

int ile[N][K];

bool czyDziala(int l, int r) {
    bool czyPoj = false;
    for (int i = 0 ; i < K ; ++i) {
        if ((ile[r][i] - (l == 0 ? 0 : ile[l-1][i])) % 2 == 1) {
            if (czyPoj) return false;
            czyPoj = true;
        }
    }
    return true;
}

int n;

bool check(int dl) {
    for (int i = dl-1; i < n; ++i) {
        if (czyDziala(i - dl + 1, i)) return true;
    }
    return false;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin >> n;
    string s;
    cin >> s;
    for (int i = 0 ; i < n; ++i) {
        for (int j = 0 ; j < K; ++j)
            if (i > 0)
                ile[i][j] = ile[i-1][j];       
        ile[i][s[i]-'a']++;
    }
    //for (int i = 0 ; i < K ; ++i)
     //   cout << (char)('a' + i) << " " ;
    //cout << "\n";
   /* for (int i = 0 ; i < n ; ++i) {
        for (int j = 0; j < K ; ++j) {
            cout << ile[i][j] << " ";
        }
        cout << "\n";
    }*/
    
    int p = 1, kon = n;
    
    while (p < kon) {
        int mid = (p + kon) / 2;
        if (check(mid)) p = mid +1 ;
        else kon = mid - 1;
    }
    if (check(p)) cout << p << "\n";
    else cout << p-1 << "\n";
}