N = int(input())
S = input().strip()

zero = 0
one = 0
max_diff = 0  # 0の数 - 1の数 の最大値

for c in S:
    if c == '0':
        zero += 1
    else:
        one += 1
    # 現在までに 0が1より何個多いか（良い文字列違反度）
    diff = zero - one
    if diff > max_diff:
        max_diff = diff

print(max_diff)