#include <iostream>
using namespace std;
#define M 3000000
int arr[M];
unsigned pows[30];

int main(){ios::sync_with_stdio(false);
    for(int i=0; i<M; i++)
        arr[i] = 999999;
    pows[0] = 0;
    pows[1] = 1;
    for(int i=2; i<30 ;i++)
    {
        pows[i] = pows[i-1]*2;
    }
    int n;
    cin >> n;
    string s; cin >> s;
    
    unsigned idx = 0;
    // idx = idx^pows[c-'a'+1];
    arr[0]  = 0;
    char c;
    int maxlen = 0;
    for(int i=0; i<n; i++) {
        c = s[i];
        //cout << idx << " " << c << " " <<c-'a'+1 << " " << pows[c-'a'+1]<< endl;
        idx = idx^pows[c-'a'+1];
       
        //cout << idx << endl;

        for(int j=0; j<21 ;j++)
        {
            unsigned tmp = idx^(pows[j]);
            //cout << "tmp " << tmp << endl;
            //cout << "maxlen " << maxlen << endl;
            maxlen  = max(maxlen, i-arr[tmp]);
        }
        arr[idx]=min(arr[idx], i+1);
    }
    cout << maxlen+1<< endl;

}