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<bits/stdc++.h>
using namespace std;
#define KIND 26
int main()
{
    int N;
    cin >> N;
    char S[N+3];
    cin >> S;
    int prev[KIND] = {0}, next[KIND] = {0};
    for(int i = 0; i < N; ++i) next[S[i] - 'a']++;
    int common = 0;
    for(int cur = 0; cur < N; ++cur) {
        int res = 0;
        char tmp = S[cur];
        ++prev[tmp - 'a']; --next[tmp - 'a'];
        for(int i = 0; i < KIND; ++i) 
            if(prev[i] > 0 && next[i] > 0) ++res;
        if(res > common) common = res;
    }
    cout << common << endl;
    return 0;
}