/**
 * 这题不能用队列来做。反例："[(][)]"
 * */
#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>

using namespace std;

const int N = 110, INF = 0x7fffffff; // INF 表示 int 数据的最大值
int f[N][N];

bool comparedChar(char a, char b) {
    if (a == '[' && b == ']') return true;
    if (a == '(' && b == ')') return true;
    return false;
}

string s;

int main()
{
    cin >> s;

    int n = s.length() - 1;
    for (int len = 1; len <= s.length(); ++len) {
        for (int i = 0; i + len - 1 <= n; ++i) {
            int j = i + len - 1;
            f[i][j] = INF; // f[i][j]默认值是0，需要改成 INF，因为我们使用了min() 函数
            if (comparedChar(s[i], s[j])) {
                f[i][j] = f[i + 1][j - 1];
            }
            f[i][j] = min(f[i][j - 1] + 1, f[i][j]);
            f[i][j] = min(f[i][j], f[i + 1][j] + 1);

            for (int k = i; k < j; ++k) {
                f[i][j] = min(f[i][j], f[i][k] + f[k + 1][j]);
            }
        }
    }

    printf("%d\n", f[0][n]);
}