#include<bits/stdc++.h>
#define ll long long
#define ld long double
#define fi first
#define se second
#define pll pair<ll, ll>
#define INF (1ll << 60)
#define ppl pair<pll, pll>
#define vi vector<int>
#define vl vector<ll>
#define vvl vector<vl>
#define FOR(i,a,b) for(ll i=a;i<b;++i)
#define pb push_back
#define ALL(X) X.begin(),X.end()
#define endl (char)10
using namespace std;

void manacher(int n , string& a , string &c , vi & P){
    for(int i=0;i<n;i++){
        c.push_back(a[i]);
        c.push_back('#');
    }
    c[2*n-1] = '$';

    for(int i=1,k=0;i<2*n;i++){
        if(k+P[k]>i){
            P[i] = max(1 , min(P[2*k-i] , k+P[k]-i));
        }
        while(P[i] <= i && c[i+P[i]]==c[i-P[i]]){
            P[i]++;
        }
        if(i+P[i] > k+P[k]){
            k=i;
        }
    }
}

int main() {
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);

    int n;
    cin>>n;
    string test;
    cin>>test;
    string nTest;
    vi P(2*n , 1);
    manacher(n , test , nTest , P);

    // cout << nTest << endl;
    // for(int i=0;i<P.size();i++){
    //     cout<<P[i];
    // }
    // cout << endl;

    int best_i=2*n-2;
    for(int i=2*n-2;i>=0;i--){
        if(i+P[i] == 2*n-1 && P[i]>1){
            best_i = i;
        }
    }

    int res=0;
    for(int l = best_i-P[best_i];l>=0;l--){
        if(nTest[l]!='#' && nTest[l]!='$'){
            res++;
        }
    }

    cout << res << endl;



}