def min_operations_to_good_string(n, s):
    operations = 0
    zero_count = 0
    one_count = 0

    for i in range(n):
        if s[i] == '0':
            zero_count += 1
        else:
            one_count += 1

        if zero_count >= one_count:
            operations += 1
            zero_count -= 1
            one_count += 1

    return operations

if __name__ == "__main__":
    n = int(input())
    s = input().strip()
    print(min_operations_to_good_string(n, s))