Problem:
Score : 200 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.
We will cut this string at one position into two strings X and Y.
Here, we would like to maximize the number of different letters contained in both X and Y.
Find the largest possible number of different letters contained in both X and Y when we cut the string at the optimal position.

Constraints

2 \leq N \leq 100

|S| = N

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the largest possible number of different letters contained in both X and Y.

Sample Input 1

6
aabbca

Sample Output 1

2

If we cut the string between the third and fourth letters into X = aab and Y = bca, the letters contained in both X and Y are a and b.
There will never be three or more different letters contained in both X and Y, so the answer is 2.

Sample Input 2

10
aaaaaaaaaa

Sample Output 2

1

However we divide S, only a will be contained in both X and Y.

Sample Input 3

45
tgxgdqkyjzhyputjjtllptdfxocrylqfqjynmfbfucbir

Sample Output 3

9

Solution in Kotlin (1.0.0) (judge verdict: Accepted)

fun main(arg: Array<String>){
    val n = readLine()!!.toInt()
    val s = readLine()!!

    var ans = 0
    for(i in 1 until n){
        var max = 0
        val s1 = s.substring(0, i).toCharArray().distinct()
        val s2 = s.substring(i, n).toCharArray().distinct()

        for (j in s1){
            for(k in s2){
                if (j == k) max++
            }
        }
        if(ans < max) ans = max
    }
    println(ans)
}