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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define endl "\n"
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef pair<ll, ll> PP;
#define rep(i, n) for(ll i = 0; i < ll(n); i++)
#define rrep(i, n) for(ll i = n - 1; i > -1; i--)
#define all(v) v.begin(), v.end()
#define pb push_back
#define fi first
#define se second
#define debug(V) rep(i, V.size()) cout << V[i] << " ";
const ll INF = 1LL << 61;
const ll MOD = 1000000007 /*988244353*/;
const ll MAX_N = 500010;
ll a, b, c, d, e, f, h, x, y, z, p, q, m, n, t, r, k, w, l, ans, i, j;
string S, T;
vl A, B;
void solve() {
    n = S.length();
    rep(i, n) {
        vl A(26, 0), B(26, 0);
        rep(j, n) {
            a = 0;
            if(j <= i)
                A[S[j] - 'a']++;
            else
                B[S[j] - 'a']++;
        }

        rep(j, 26) {
            if(A[j] * B[j])
                a++;
        }
        ans = max(ans, a);
    }

    cout << ans << endl;
}
int main() {
    // cout<<fixed<<setprecision(15);
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> n;
    cin >> S;
    solve();
}