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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"fmt"
	"strings"
)

func main() {
	var n int
	var s string
	fmt.Scan(&n)
	fmt.Scan(&s)

	ans := 0
	for i := 0; i < n; i++ {
		cnt := 0
		for c := 'a'; c <= 'z'; c++ {
			left, right := false, false
			if strings.Index(s[:i+1], string(c)) > -1 {
				left = true
			}
			if strings.Index(s[i+1:], string(c)) > -1 {
				right = true
			}
			if left && right {
				cnt++
			}
		}
		if ans < cnt {
			ans = cnt
		}
	}
	fmt.Println(ans)
}