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 (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#define ll long long
#define rep(i,l,r) for(ll i=(l);i<(r);i++)
#define max(p,q) ((p)>(q)?(p):(q))
#define min(p,q) ((p)<(q)?(p):(q))
#define abs(p) ((p)>=(0)?(p):(-(p)))
int cmp(const void *a, const void *b);
int main(void){
    ll N, ANS=0; char S[105];
    scanf("%lld\n%s", &N, S);
    rep(i, 1, N){
        ll c=0;
        for(char s='a'; s<='z'; s++){
            ll L=0, R=0;
            rep(j, 0, i) if(S[j]==s) L=1;
            rep(j, i, N) if(S[j]==s) R=1;
            if(L&&R) c++;
        }
        ANS = max(ANS,c);
    }
    printf("%lld\n", ANS);
    return 0;
}
int cmp(const void *a, const void *b){
    ll A=*(ll *)a, B=*(ll *)b;
    if(A==B)return 0;
    else return A>B ? 1:-1;//昇順ソート
}