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 Julia (0.5.0) (judge verdict: Accepted)

parseInt(x) = parse(Int, x)
parseMap(x::Array{SubString{String},1}) = map(parseInt, x)
mod(x::Int,p::Int)=x%p>0?x%p:x%p+p

function main()
	p = 92709568269121
	n = readline() |> parseInt
	t = readline() |> chomp
	s = zeros(Int,n)
	for i in 1:n
		s[i] = Int(t[i])
	end
	b = 101
	c = zeros(Int,n>>1+1)
	c[1] = 1
	for i in 1:n>>1
		c[i+1] = c[i]*b%p
	end
	ll = 0
	rr = n>>1+1
	while rr-ll>1
		i = (ll+rr)>>1
		f = 0
		set = Set{Int}([])
		arch = Int[0 for i in 1:n-i+1]
		l = 0
		for j in 1:i
			l = mod(l+s[j]*c[i-j+1],p)
		end
		arch[1] = l
		for j in 2:n-i+1
			l = mod(mod(mod(l-s[j-1]*c[i],p)*b,p)+s[j+i-1],p)
			arch[j] = l
			if j>i
				push!(set,arch[j-i])
			end
			if l in set
				f = 1
				break
			end
		end
		if f == 1
			ll = i
		else
			rr = i
		end
	end
	println(ll)
end

main()