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)

char s[111];
n,ans,cnt[26],now;
main(){
  scanf("%d%s",&n,s);
  for(int i=1;i<n;i++){
    for(int j=0;j<26;j++)cnt[j]=0;
    for(int j=0;j<i;j++)cnt[s[j]-'a']++;
    now=0;
    for(int j=i;j<n;j++)now+=!!cnt[s[j]-'a'],cnt[s[j]-'a']=0;
    ans=fmax(ans,now);
  }
  printf("%d",ans);
}