n = int(input())
seq = input()


def check_validity(mugs):
    counter = 0
    total_len = 0
    for k, v in mugs.items():
        total_len += v
        if v % 2 == 1:
            counter += 1
            if counter == 2:
                return False
    print(total_len)
    exit(0)


def parse_dict(seq):
    parsed = {}
    for char in seq:
        parsed[char] = parsed.get(char, 0) + 1
    
    return parsed

m = [[0]*(n-1)]
m[0].append(parse_dict(seq))
check_validity(m[0][-1])

for i in range(n-2, -1, -1):
    for j in range(0, n-i - 1):
        y = i + j
        x = j
        d = m[x][y + 1]
        m[x][y] = dict(d)

        m[x][y][seq[y+1]] -= 1
        check_validity(m[x][y])

    j = n - i - 1
    y = i + j
    x = j

    m.append([0] * (n - 1))

    d = m[x - 1][y]
    m[x].append(dict(d))
    m[x][y][seq[x - 1]] -= 1
    check_validity(m[x][y])