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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <vector>
#include <climits>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <bitset>
#include <utility>
#include <numeric>
#include <queue>
#include <stack>

using ll = long long;
using namespace std;

constexpr int MOD = 1e9 + 7;
constexpr ll MOD_LL = ll(1e9) + 7;

int main(void) {
	int n;
	string s;
	cin >> n >> s;
	
	int ans = 0;
	for(int i = 1; i < n - 1; ++i) {
		string tmp = s.substr(0, i);
		string tmp2 = s.substr(i, n - i);
		
		map<char, int> mp1, mp2;
		for(int i = 0; i < tmp.size(); ++i) {
			mp1[tmp[i]]++;
		}
		
		for(int i = 0; i < tmp2.size(); ++i) {
			mp2[tmp2[i]]++;
		}
		
		int cnt = 0;
		for(char c = 'a'; c <= 'z'; ++c) {
			if( mp1[c] > 0 && mp2[c] > 0 ) cnt++;
		}
		
		ans = max(ans, cnt);
	}
	
	cout << ans << endl;
	
	return 0;
}