Problem:
Score : 500 points

Problem Statement

Given is a string S of length N.

Find the maximum length of a non-empty string that occurs twice or more in S as contiguous substrings without overlapping.

More formally, find the maximum positive integer len such that there exist integers l_1 and l_2 ( 1 \leq l_1, l_2 \leq N - len + 1 ) that satisfy the following:

l_1 + len \leq l_2

S[l_1+i] = S[l_2+i] (i = 0, 1, ..., len - 1)

If there is no such integer len, print 0.

Constraints

2 \leq N \leq 5 \times 10^3

|S| = N

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the maximum length of a non-empty string that occurs twice or more in S as contiguous substrings without overlapping. If there is no such non-empty string, print 0 instead.

Sample Input 1

5
ababa

Sample Output 1

2

The strings satisfying the conditions are: a, b, ab, and ba. The maximum length among them is 2, which is the answer.
Note that aba occurs twice in S as contiguous substrings, but there is no pair of integers l_1 and l_2 mentioned in the statement such that l_1 + len \leq l_2.

Sample Input 2

2
xy

Sample Output 2

0

No non-empty string satisfies the conditions.

Sample Input 3

13
strangeorange

Sample Output 3

5

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Collections;

static class Extensions
{
    public static int ToInt(this string s) => int.Parse(s);
    public static long ToLong(this string s) => long.Parse(s);
    public static char ToChar(this string s) => char.Parse(s);
    public static double ToDouble(this string s) => double.Parse(s);
    public static int[] ToIntArray(this string s) => s.Replace(',', ' ').Split(' ').Select(x => x.ToInt()).ToArray();
    public static long[] ToLongArray(this string s) => s.Replace(',', ' ').Split(' ').Select(x => x.ToLong()).ToArray();
    public static double[] ToDoubleArray(this string s) => s.Replace(',', ' ').Split(' ').Select(x => x.ToDouble()).ToArray();
    public static Queue<T> ToQueue<T>(this IEnumerable<T> seq) => new Queue<T>(seq);
    public static Stack<T> ToStack<T>(this IEnumerable<T> seq) => new Stack<T>(seq);
    public static HashSet<T> ToHashSet<T>(this IEnumerable<T> seq) => new HashSet<T>(seq);
}

static class MyMath
{
    static public long GCD(long a, long b) => (a < b) ? GCD(b, a) : ((b == 0) ? a : GCD(b, a % b));
    static public long LCM(long a, long b) => (a > b) ? (a / GCD(a, b) * b) : (b / GCD(a, b) * a);
    static private readonly long _m = 1000000000 + 7;
    static public long Mod(long val) => (val % _m + _m) % _m;
    static private long ExtGCD(long a, long b, ref long x, ref long y) => (b == 0) ? (a + (x = 1) * 0 + (y = 0) * 0) : (ExtGCD(b, a % b, ref y, ref x) + (y -= a / b * x) * 0);
    static private long ModInverseInner(long a, long dummy1 = 0, long dummy2 = 0) => ExtGCD(a, _m, ref dummy1, ref dummy2) * 0 + Mod(dummy1);
    static public long ModInverse(long a) => ModInverseInner(a, 0, 0);
}

class Program
{
    static string[] ReadLines(int n) => Enumerable.Range(0, n).Select(s => Console.ReadLine()).ToArray();

    static void Main()
    {
        int N = Console.ReadLine().ToInt();
        string S = Console.ReadLine();

        int max = 0;
        for (int i = 1; i <= N / 2; i++)
        {
            //長さiの部分文字列を全部チェック
            HashSet<string> set = new HashSet<string>();
            for (int j = 0; j < N; j++)
            {
                if (j + i - 1 > S.Length - 1)
                {
                    break;
                }

                string str = S.Substring(j, i);
                if (set.Contains(str))
                {
                    max = i;
                    break;
                }
                else
                {
                    set.Add(str);
                }
            }
        }

        Console.WriteLine(max);
    }    
}