i = int(input())
s = input()

s = s[:i]

def pos(str, c):
    arr = []
    for k in range(len(str)):
        if str[k] == c:
            arr.append(k)
    return arr

def sim(str):

    map = {
        'a': False,
        'b': False,
        'c': False,
        'd': False,
        'e': False,
        'f': False,
        'g': False,
        'h': False,
        'i': False,
        'j': False,
        'k': False,
        'l': False,
        'm': False,
        'n': False,
        'o': False,
        'p': False,
        'q': False,
        'r': False,
        's': False,
        't': False
    }
    for i in str:
        map[i] = not map[i]
    sum = 0
    for i in map:
        sum += int(map[i])
    if sum > 1:
        return 0
    return len(str)


arr = []
l = 0
sa = sim(s) 
if sa > 0:
    print(sa)
    exit(0)
arr.insert(0, (0, len(s) - 1))
while l == 0:
    tmp = arr.pop()
    l = sim(s[tmp[0]: tmp[1]])
    arr.insert(0, (tmp[0] + 1, tmp[1]))
    arr.insert(0, (tmp[0], tmp[1] - 1 ))
    



print(l)