//
// 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;



int main() {
    ios_base::sync_with_stdio(0);
    f(i,0,26)
    {
        occs.push_back(vector<int>());
    }
    int size;
    cin >> size;
    string s;
    cin >> s;
    f(i,0,size)
    {
        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(occs[i].size() - 1);
    }
    int lastletter = s[s.length()-1] - 'a';
    int position = size - 1;
    int longest = 0;
    bool correct = true;
    while(position >= 0)
    {
        correct = true;
        b(i, size -1, (size + position)/2)
        {
            if(s[i] != s[size - 1 + position - i])
            {
                correct = false;
                letterptrs[lastletter]--;
                if(letterptrs[lastletter] == -1)
                {
                    position = -1;
                }
                else
                {
                    position = occs[lastletter][letterptrs[lastletter]];
                }
                break;
            }
        }
        if(correct)
        {
            longest = size - position;
            letterptrs[lastletter]--;
            if(letterptrs[lastletter] == -1)
            {
                position = -1;
            }
            else
            {
                position = occs[lastletter][letterptrs[lastletter]];
            }
        }
    }

    cout << size - longest;


   return 0;
}