def min_operations_to_good_string(N, S):
    diff = 0  # 0の数 - 1の数
    ops = 0   # 操作回数

    for ch in S:
        if ch == '0':
            diff += 1
        else:
            diff -= 1
        
        # もし0の数が多くなってしまったら、1に変える操作を行う
        if diff > 0:
            ops += 1
            diff -= 1  # 仮に0を1に変えたとする（差を減らす）

    return ops

# 入力例の処理
N = int(input())
S = input()
print(min_operations_to_good_string(N, S))