paliny

//#include<bits/stdc++.h>
#include<iostream>
#include<fstream>
#include<vector>
#include<string>

#define long long long
#define nln '\n'

using namespace std;

// GLobal variables: f1, f2,

fstream f1,f2;

inline void openf()
{
    f1.open("paliny.inp", ios:: in);
    f2.open("paliny.out", ios:: out);
}

inline void closef()
{
    f1.close();
    f2.close();
}

long n;
string str;

void data()
{
    f1.tie(0)->sync_with_stdio(0);
    f2.tie(0)->sync_with_stdio(0);
    cin >> n;
    cin >> str;
}
long mav = -1e9;

void browse(long i, long j)
{
    long cou;
    if (i != j)
        cou = 0;
    else
        cou = -1;

    long lef = i, rig = j;
    while (lef >= 0 && rig < n && str[lef] == str[rig])
    {
        cou += 2;
        --lef; ++rig;
    }
    if (cou > mav)
        mav = cou;
}

void process()
{
    long i = n/2, j = n/2 + 1;
    while (i > mav/2 && j < n - mav/2)
    {
        //cout << i << " - " << j << nln;
        browse(i, i);
        browse(i-1, i);
        browse(j, j);
        browse(j, j+1);
        --i;
        ++j;
        //cout << "mav: " << mav << nln;
    }
}

void view()
{
    cout << mav << nln;
}

int main()
{
    openf();
    data();
    process();
    view();
    closef();
    return 0;
}