#include<bits/stdc++.h>
using namespace std;

#define ll long long
#define nl "\n"

void files(){
    ios_base::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL);
    #ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
    #endif
}

struct Hash{
    const static int mod = 1e9 + 7,p1 = 31,p2 = 37;
    int n;
    vector<int> h1,h2,pw1,pw2;
    Hash(string &s){
        n = s.size();
        h1 = vector<int>(n + 1,0),h2 = vector<int>(n + 1,0);
        pw1 = vector<int>(n + 1,1),pw2 = vector<int>(n + 1,1);
        for(int i = 1; i <= n; i++){
            h1[i] = (1LL * h1[i - 1] * p1 + s[i - 1]) % mod;
            h2[i] = (1LL * h2[i - 1] * p2 + s[i - 1]) % mod;
            pw1[i] = 1LL * pw1[i - 1] * p1 % mod;
            pw2[i] = 1LL * pw2[i - 1] * p2 % mod;
        }
    }

    pair<int,int> get(int l,int r){
        int a = (h1[r] - 1LL * h1[l - 1] * pw1[r - l + 1] % mod + mod) % mod;
        int b = (h2[r] - 1LL * h2[l - 1] * pw2[r - l + 1] % mod + mod) % mod;
        return {a,b};
    }
};


void solve(){
    int n; cin>>n;
    string s; cin>>s;
    string t = s;
    reverse(t.begin(),t.end());
    Hash h1(s),h2(t);

    int ans = 0;
    int res = 1;
    int l = 0, r = n;
    while(l<=r){
        int m = (l + r) / 2;
        bool ok = false;
        for(int i = m+1; i+m <= n and i-m>=1; i++){
            int left = i-m,right = i+m;
            auto a = h1.get(left,right);
            auto b = h2.get(n-right+1,n-left+1);
            if(a == b){
                ok = true;
                break;
            }
        }
        if(ok){
            ans = m;
            res = max(res,2*ans+1);
            l = m + 1;
        }else r = m - 1;
    }


    l = 0, r = n, ans = 0;
    while(l<=r){
        int m = (l + r) / 2;
        bool ok = false;
        for(int i = m+1; i+m < n and i-m>=1; i++){
            int left = i-m,right = i+m+1;
            // cout<<left<<" "<<right<<' '<<m<<nl;
            auto a = h1.get(left,right);
            auto b = h2.get(n-right+1,n-left+1);
            if(a == b){
                ok = true;
                break;
            }
        }
        if(ok){
            ans = m;
            res = max(res,2*ans+2);
            l = m + 1;
        }else r = m - 1;
    }


    cout<<res<<nl;

}

int main(){
    files();
    int t = 1;
    // cin>>t;
    while(t--) solve();

    return 0;
}