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 9.2.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
typedef long long ll;
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define max(a,b) (a>b?a:b)

int main(){
    int n;scanf("%d",&n);
    char s[105];scanf("%s",s);
    int tmpa=0;
    rep(i,n-1){
        int cl[30]={0},cr[30]={0};
        rep(j,i+1){
            cl[s[j]-'a']++;
        }
        rep(j,n-(i+1)){
            cr[s[j+i+1]-'a']++;
        }
        int tmp = 0;
        rep(j,'z'-'a'+1){
            if(cl[j]&&cr[j])tmp++;
        }
        tmpa=max(tmpa,tmp);
    }
    printf("%d",tmpa);
}