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>
const int maxn = 100;
typedef long long LL;
int mp[36];
char a[105];
int vis[28];
int main(){
	int n;
	scanf("%d",&n);
	getchar();
	gets(a);
	int ans = 0,pos = 0;
	for(int i = 0;i<n;i++){
		mp[a[i]-'a']++;
		pos = 0;
		for(int k = 0;k<28;k++)
			vis[k] = 0;
		for(int j = i+1;j<n;j++){
			if(vis[a[j]-'a']) continue;
			if(mp[a[j]-'a']) {
				vis[a[j]-'a'] = 1;
				pos++;
			}
		}
		if(pos > ans) ans = pos;
	}
	printf("%d\n",ans);
	return 0;
}