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

int main(){
    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;
    }
    char c;
    unsigned idx = 0;
    int n;
    scanf("%d", &n);
    while(1)
    {
        c = getchar();
        if(c >= 'a')
            break;
    }
    idx = idx^pows[c-'a'+1];
    arr[0]  =0;
    arr[idx] = 1;
    unsigned tmp = 0;
    int maxlen = 0;
    for(int i=2; i<=n; i++)
    {
        c = getchar();
        //cout << idx << " " << c << " " <<c-'a'+1 << " " << pows[c-'a'+1]<< endl;
        idx = idx^pows[c-'a'+1];

        maxlen = max(maxlen, i-arr[idx]);
        arr[idx]=min(arr[idx], i);
        //cout << idx << endl;

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

}