//
// Created by cteam012 on 12/1/19.
//
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
#define f(i,a,b) for(int i = (a); i < (b);++i)
#define b(i,a,b) for(int i = (a); i >= (b);--i)

vector<vector<int>> occs(26);



int main() {
    //vector<vector<int>> occs(26);
    ios_base::sync_with_stdio(0);
    f(i,0,26)
    {
        occs[i] = vector<int>();
    }
    int size;
    cin >> size;
    string s;
    cin >> s;
    f(i,0,size)
    {
        //cout << s[i] << ';' << (s[i] - 'a') << "|";
        occs[s[i]-'a'].push_back(i);
    }
    f(i,0,26)
    {
        sort(occs[i].begin(), occs[i].end());
    }
    vector<int> letterptrs;
    f(i,0,26)
    {
        letterptrs.push_back(0);
    }
    int position = 0;
    int longest = 0;
    bool correct = true;
    while(position < size)
    {
        correct = true;
        f(i, position, (size + position)/2)
        {
            if(s[i] != s[size - 1 + position - i])
            {
                int lastpos = size - 1 + position - i;
                int lastlet = s[lastpos] - 'a';
                correct = false;

                while(occs[lastlet][letterptrs[lastlet]] < i)
                {
                    letterptrs[lastlet]++;
                }
                position = occs[lastlet][letterptrs[lastlet]] - i + position;
                break;
            }
        }
        if(correct)
        {
            longest = size - position;
            break;
        }
    }

    cout << size - longest;


   return 0;
}