def solve():
    N = int(input())
    S = input()

    balance = 0
    count = 0

    for c in S:
        if c == '1':
            balance += 1
        else:  # c == '0'
            balance -= 1
        if balance < 0:
            count += 1
            balance += 1  # 0を1に変えたとして補正

    print(count)