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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

INTEGER N
CHARACTER(100) S
CHARACTER(26)::A="abcdefghijklmnopqrstuvwxyz"
INTEGER B,P
INTEGER M,U
READ*,N,S
P=0
DO I=1, N-1
  B=0
  DO J=1,26
    M=SCAN(S,A(J:J))
    IF(M==0)CYCLE
    U=SCAN(S,A(J:J),.TRUE.)
    IF( M<=I .AND. I<U )B=B+1
  END DO
  P=MAX(P,B)
END DO
PRINT"(I0)",P
END