#include <iostream>
#include <vector>
#include <string>

using namespace std;

string orig_str;

int pocet_lichy(vector<int> & pole,int vymaz, int & lichy_pocet)
{
    int p_l = 0;
    pole[vymaz]--;
    for(int i = 0; i < 20; i++)
    {
        if(pole[i] % 2 == 1)
            p_l++;
    }
    lichy_pocet = p_l;
}

int rekurzivka(vector<int> pole,int left, int right,int vymaz,int all_count,int liche_count,bool first_time )
{
    int rek1 = 0, rek2 = 0;

    if(all_count == 1)
        return 1;

    if(!first_time)
        pocet_lichy(pole,vymaz,liche_count);
    else
        first_time = false;




    if((all_count % 2 == 1) && (liche_count == 1) )
        return all_count;
    else if ((all_count % 2 == 0) && (liche_count == 0) )
        return all_count;
    else
    {
        all_count--;
        rek1 = rekurzivka(pole,left+1,right,orig_str[left]-97,all_count,liche_count,false);
        rek2 = rekurzivka(pole,left,right-1,orig_str[right]-97,all_count,liche_count,false);
    }
    if(rek1 > rek2 )
        return rek1;
    else
        return rek2;

}

int main() {

    vector<int> a(20);
    int liche_counter = 0;
    int count;
    int rek1,rek2;

    cin >> count;
    cin >> orig_str;


    for(int i = 0; i < 20; i++)
        a[i] = 0;


    for(int i = 0; i < count; i++)
        a[orig_str[i] - 97]++;

    for(int i = 0 ; i < 20; i++)
    {
        if(a[i] % 2 == 1)
            liche_counter++;
    }

    rek1 = rekurzivka(a,0,count-1,orig_str[0]-97,count,liche_counter,true);
    //rek2 = rekurzivka(a,0,count-1,orig_str[count - 1]-97,count,liche_counter,true);


    cout << rek1 << endl;
    return 0;
}