#include <iostream>
#include <vector>
using namespace std;
int manaker(string s, int n){
    vector <int> p(n);
    int c=0;
    int l=0;
    for (int i=0; i<n; i++){
        while (i-p[i]>0 && s[i-p[i]-1]==s[i+p[i]+1]){
            ++p[i];
        }
    }
    int maximum=0;
    for (int i=0; i<n; i++){
        if(i%2==1){
            if(2*(p[i]/2)+1>maximum){
                maximum=2*(p[i]/2)+1;
            }
        }
        else{
            if (2*(p[i]/2)>maximum){
                maximum=2*(p[i]/2);
            }
        }
    }
    return maximum;
}
int main(){
    int n;
    cin>>n;
    string s;
    cin>>s;
    string c;
    for (int i=0; i<2*n+1; i++){
        if(i%2==1){
            int x=i/2;
            c.push_back(s[x]);
        }else{
            c.push_back('.');
        }
    }
    int answer=manaker(c, 2*n+1);
    for (int i=1; i<2*n+1; i+=2){
        for (int j=1; j<2*n+1; j+=2){
            string k=c;
            k[i]=c[j];
            if (manaker(k, 2*n+1)>answer){
                answer=manaker(k, 2*n+1);
            }
        }
    }
    cout<<answer<<endl;
}