CF1860D.Balanced String

You are given a binary string $s$ (a binary string is a string consisting of characters 0 and/or 1).

Let's call a binary string balanced if the number of subsequences 01 (the number of indices $i$ and $j$ such that $1 \le i \lt j \le n$, $s_i=0$ and $s_j=1$) equals to the number of subsequences 10 (the number of indices $k$ and $l$ such that $1 \le k \lt l \le n$, $s_k=1$ and $s_l=0$) in it.

For example, the string 1000110 is balanced, because both the number of subsequences 01 and the number of subsequences 10 are equal to $6$. On the other hand, 11010 is not balanced, because the number of subsequences 01 is $1$, but the number of subsequences 10 is $5$.

You can perform the following operation any number of times: choose two characters in $s$ and swap them. Your task is to calculate the minimum number of operations to make the string $s$ balanced.

给你一个二进制字符串 $s$（二进制字符串是由字符 0 和/或 1 组成的字符串）。

我们称一个二进制字符串是平衡的，如果其中子序列 01 的数量（即满足 $1 \le i \lt j \le n$、$s_i=0$ 且 $s_j=1$ 的下标对 $(i, j)$ 的个数）等于子序列 10 的数量（即满足 $1 \le k \lt l \le n$、$s_k=1$ 且 $s_l=0$ 的下标对 $(k, l)$ 的个数）。

例如，字符串 1000110 是平衡的，因为子序列 01 的数量和子序列 10 的数量均为 $6$。而 11010 不是平衡的，因为子序列 01 的数量为 $1$，但子序列 10 的数量为 $5$。

你可以执行以下操作任意多次：在 $s$ 中任选两个字符并交换它们。你的任务是计算使字符串 $s$ 变为平衡字符串所需的最少操作次数。

The only line contains the string $s$ ($3 \le |s| \le 100$) consisting of characters 0 and/or 1.

Additional constraint on the input: the string $s$ can be made balanced.

仅有一行，包含字符串 $s$（$3 \le |s| \le 100$），其字符仅由 0 和/或 1 组成。

输入的额外约束：字符串 $s$ 可以被调整为平衡的。

Print a single integer — the minimum number of swap operations to make the string $s$ balanced.

输出一个整数——使字符串 $s$ 平衡所需的最少交换操作次数。

In the first example, the string is already balanced, the number of both 01 and 10 is equal to $1$.

In the second example, the string is already balanced, the number of both 01 and 10 is equal to $6$.

In the third example, one of the possible answers is the following one: 11010 $\rightarrow$ 01110. After that, the number of both 01 and 10 is equal to $3$.

In the fourth example, one of the possible answers is the following one: 11001100 $\rightarrow$ 11001010 $\rightarrow$ 11000011. After that, the number of both 01 and 10 is equal to $8$.

在第一个例子中，该字符串已经是平衡的，其中子串 01 和 10 的数量均为 $1$。

在第二个例子中，该字符串已经是平衡的，其中子串 01 和 10 的数量均为 $6$。

在第三个例子中，一种可能的答案如下：11010 $\rightarrow$ 01110。变换后，子串 01 和 10 的数量均为 $3$。

在第四个例子中，一种可能的答案如下：11001100 $\rightarrow$ 11001010 $\rightarrow$ 11000011。变换后，子串 01 和 10 的数量均为 $8$。