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: Wrong Answer)

#include <stdio.h>
#include <string.h>

int main(void) {
	int n;
	char c[101];
	int pair=0;
	int tmp=0, last=0;
	scanf("%d", &n);
	for (int i = 0; i < n; i++) {
		for (int j = i + 1; j < n; j++) {
			if (c[i] == c[j]) {
				if (tmp != 0) {
					last = tmp;
					c[tmp] = '0';
					tmp = j;
				}
				else {
					last = tmp;
					tmp = j;
				}
			}
		}
	}
	for (int i = 0; i < n; i++) {
		if (c[i] != '0') pair += 1;
	}
	printf("%d", pair/2);
	return 0;
}