def main():
	N = int(input())
	seq = input().strip()
	
	numbers = [dict() for _ in range(N)]
	for i, c in enumerate(seq):
		numbers[i]['odds'] = 1
		numbers[i][c] = 1
	max_len = 0
	for size in range(2, N+1):
		for i in range(N-1, size-2, -1):
			numbers[i] = add(numbers[i-1], seq[i])
			if not numbers[i]['odds'] or numbers[i]['odds'] == 1:
				max_len = size
	print(max_len)

def add(d, c):
	new = d.copy()
	if c not in new:
		new[c] = 0
	new[c] += 1
	if new[c] % 2 == 1:
		new['odds'] += 1
	else:
		new['odds'] -= 1
	return new


main()