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.
N = int(input())
S = input()
temp=0
for i in range(N-1):
    S1=S[0:i+1]
    S2=S[i+1:N]

    kaburi = [s for s in S1 if s in S2]

    if len(kaburi)>temp:
        temp = len(kaburi)
print(temp)
N = int(input())
S = input()
temp=0
for i in range(N-1):
    S1=S[0:i+1]
    S2=S[i+1:N]
#    print(S1 + " " + S2)
    kaburi=[]
    for s in S1:
        if s in S2 and s not in kaburi:
            kaburi.append(s)
    if len(kaburi)>temp:
        temp = len(kaburi)
print(temp)